diff --git a/wordcloud/wordcloud.py b/wordcloud/wordcloud.py
index b42961a..c2b9d98 100644
--- a/wordcloud/wordcloud.py
+++ b/wordcloud/wordcloud.py
@@ -466,6 +466,8 @@ class WordCloud(object):
 
         # start drawing grey image
         for word, freq in frequencies:
+            if freq == 0:
+                continue
             # select the font size
             rs = self.relative_scaling
             if rs != 0:

generate_from_frequencies() raise ZeroDivisionError when there're more than one zero in the data
#### Description
Similar Issue: [Issue 308](https://github.com/amueller/word_cloud/issues/308)

At line 464 in wordcloud.py:
```
if rs != 0:
                font_size = int(round((rs * (freq / float(last_freq))
                                       + (1 - rs)) * font_size))
```

If last_freq == 0 (more than one zero in the data), ZeroDivisionError will be raised.

And I'm using generate_from_frequencies() for plotting not only frequency data, but other statistics, such as p-values, chi-square, etc. Decimals are fine, too many zeros would raise the error. I haven't tested negative values (in some cases negative values do make sense, for example in statistics), so I'm not sure whether using negative values as input data will cause any other problems. 

The workaround I'm using now is to manually remove all zeros in my data (and negative values too, I suppose), but there might be not enough words in the figure. Another workaround is to replace all zeros with a very small number, for example 0.0000000001, which produces better results.

Thanks in advance.

#### Steps/Code to Reproduce

Example:
```
import wordcloud

word_cloud = wordcloud.WordCloud()

word_cloud.generate_from_frequencies({'test': 1, 'test1': 0, 'test2': 2}) # OK
word_cloud.generate_from_frequencies({'test': 1, 'test1': 0, 'test2': 0}) # Error
```

#### Versions
Windows-10-10.0.17134-SP0
Python 3.7.1 (v3.7.1:260ec2c36a, Oct 20 2018, 14:57:15) [MSC v.1915 64 bit (AMD64)]
matplotlib 3.0.2
wordcoud 1.5.0
diff --git a/test/test_wordcloud.py b/test/test_wordcloud.py
index a111562..88bbadd 100644
--- a/test/test_wordcloud.py
+++ b/test/test_wordcloud.py
@@ -387,3 +387,12 @@ def test_repeat():
     frequencies = [w[0][1] for w in wc.layout_]
     # check that frequencies are sorted
     assert np.all(np.diff(frequencies) <= 0)
+
+
+def test_zero_frequencies():
+
+    word_cloud = WordCloud()
+
+    word_cloud.generate_from_frequencies({'test': 1, 'test1': 0, 'test2': 0})
+    assert len(word_cloud.layout_) == 1
+    assert word_cloud.layout_[0][0][0] == 'test'

pip install -e .
parse_log_pytest
requirements.txt
pytest pytest-cov pytest-sugar
apt-get update apt-get install -y gcc
3.6
requirements.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
attrs==22.2.0
certifi==2021.5.30
coverage==6.2
cycler==0.11.0
importlib-metadata==4.8.3
iniconfig==1.1.1
kiwisolver==1.3.1
matplotlib==3.3.4
numpy==1.19.5
packaging==21.3
Pillow==8.4.0
pluggy==1.0.0
py==1.11.0
pyparsing==3.1.4
pytest==7.0.1
pytest-cov==4.0.0
pytest-sugar==0.9.6
python-dateutil==2.9.0.post0
six==1.17.0
termcolor==1.1.0
tomli==1.2.3
typing_extensions==4.1.1
-e git+https://github.com/amueller/word_cloud.git@64ff55ea10751deac3381fbc268c47827704a2c3#egg=wordcloud
zipp==3.6.0

name: word_cloud
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - certifi=2021.5.30=py36h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.3=he6710b0_2
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=1.1.1w=h7f8727e_0
  - pip=21.2.2=py36h06a4308_0
  - python=3.6.13=h12debd9_1
  - readline=8.2=h5eee18b_0
  - setuptools=58.0.4=py36h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - wheel=0.37.1=pyhd3eb1b0_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - attrs==22.2.0
      - coverage==6.2
      - cycler==0.11.0
      - importlib-metadata==4.8.3
      - iniconfig==1.1.1
      - kiwisolver==1.3.1
      - matplotlib==3.3.4
      - numpy==1.19.5
      - packaging==21.3
      - pillow==8.4.0
      - pluggy==1.0.0
      - py==1.11.0
      - pyparsing==3.1.4
      - pytest==7.0.1
      - pytest-cov==4.0.0
      - pytest-sugar==0.9.6
      - python-dateutil==2.9.0.post0
      - six==1.17.0
      - termcolor==1.1.0
      - tomli==1.2.3
      - typing-extensions==4.1.1
      - zipp==3.6.0
prefix: /opt/conda/envs/word_cloud

test/test_wordcloud.py::test_zero_frequencies
test/test_wordcloud.py::test_collocations test/test_wordcloud.py::test_plurals_numbers test/test_wordcloud.py::test_multiple_s test/test_wordcloud.py::test_empty_text test/test_wordcloud.py::test_default test/test_wordcloud.py::test_stopwords_lowercasing test/test_wordcloud.py::test_writing_to_file test/test_wordcloud.py::test_check_errors test/test_wordcloud.py::test_recolor test/test_wordcloud.py::test_random_state test/test_wordcloud.py::test_mask test/test_wordcloud.py::test_mask_contour test/test_wordcloud.py::test_single_color_func test/test_wordcloud.py::test_single_color_func_grey test/test_wordcloud.py::test_process_text test/test_wordcloud.py::test_process_text_regexp_parameter test/test_wordcloud.py::test_generate_from_frequencies test/test_wordcloud.py::test_relative_scaling_zero test/test_wordcloud.py::test_unicode_stopwords test/test_wordcloud.py::test_include_numbers test/test_wordcloud.py::test_min_word_length test/test_wordcloud.py::test_recolor_too_small test/test_wordcloud.py::test_recolor_too_small_set_default test/test_wordcloud.py::test_small_canvas test/test_wordcloud.py::test_tiny_canvas test/test_wordcloud.py::test_coloring_black_works test/test_wordcloud.py::test_repeat
wordcloud/wordcloud.py
wordcloud/wordcloud.py