groupby.quantile(<arraylike>) fails with AssertionError
#### Code Sample, a copy-pastable example if possible

```python
# Your code here
df = pd.DataFrame(np.array([10*[_%4] for _ in range(100)]))            

df.groupby(0).quantile(0.5)                                            
# Out[19]: 
#     1    2    3    4    5    6    7    8    9
# 0                                             
# 0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0
# 1  1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0
# 2  2.0  2.0  2.0  2.0  2.0  2.0  2.0  2.0  2.0
# 3  3.0  3.0  3.0  3.0  3.0  3.0  3.0  3.0  3.0

df.groupby(0).quantile([0.5,0.99])                                     
---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
<ipython-input-20-21c92d2481c9> in <module>
----> 1 df.groupby(0).quantile([0.5,0.99])

~/PycharmProjects/netsim_stats/venv/lib/python3.7/site-packages/pandas/core/groupby/groupby.py in quantile(self, q, interpolation)
   1950 
   1951             indices = np.concatenate(arrays)
-> 1952             assert len(indices) == len(result)
   1953             return result.take(indices)
   1954 

AssertionError: 

df.quantile([0.5,0.99])                                                
#        0    1    2    3    4    5    6    7    8    9
# 0.50  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5
# 0.99  3.0  3.0  3.0  3.0  3.0  3.0  3.0  3.0  3.0  3.0
                                                              
df.groupby(0)[1].quantile(0.5) 
# 0
# 0    0.0
# 1    1.0
# 2    2.0
# 3    3.0
# Name: 1, dtype: float64

df.groupby(0)[1].quantile([0.5,0.99])

---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
<ipython-input-24-ebf6ade716ff> in <module>
----> 1 df.groupby(0)[1].quantile([0.5,0.99])

~/PycharmProjects/netsim_stats/venv/lib/python3.7/site-packages/pandas/core/groupby/groupby.py in quantile(self, q, interpolation)
   1950 
   1951             indices = np.concatenate(arrays)
-> 1952             assert len(indices) == len(result)
   1953             return result.take(indices)
   1954 

AssertionError: 

```
#### Problem description

The above is a constructed minimal example.
I am not sure how much I should elaborate on the "why this is a problem".

groupby.quantile() fails with an assertion error for "larger" dataframes, smaller dataframes seem to work fine.

#### Expected Output

#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit           : None
python           : 3.7.5.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.3.15-200.fc30.x86_64
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : de_DE.UTF-8
LOCALE           : de_DE.UTF-8

pandas           : 0.25.3
numpy            : 1.17.4
pytz             : 2019.3
dateutil         : 2.8.1
pip              : 19.1.1
setuptools       : 40.8.0
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : 4.2.5
html5lib         : 1.0.1
pymysql          : None
psycopg2         : None
jinja2           : 2.10.1
IPython          : 7.2.0
pandas_datareader: None
bs4              : 4.6.3
bottleneck       : None
fastparquet      : None
gcsfs            : None
lxml.etree       : 4.2.5
matplotlib       : 3.1.2
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pytables         : None
s3fs             : None
scipy            : 1.1.0
sqlalchemy       : None
tables           : None
xarray           : None
xlrd             : None
xlwt             : None
xlsxwriter       : None


</details>
