Core dump when converting to category with duplicate column names
#### Code Sample, a copy-pastable example if possible

```python
import pandas as pd
import numpy as np
X = np.random.normal(size=(100, 2))
X_df = pd.DataFrame(X, columns=[0, 0])
X_df[0] = X_df[0].astype('category')

```
#### Problem description
Stack overflow in the Python interpreter

#### Expected Output
No core dump.

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

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.7.1.final.0
python-bits: 64
OS: Linux
OS-release: 4.15.0-46-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.23.4
pytest: 3.6.2
pip: 10.0.1
setuptools: 39.2.0
Cython: 0.29.2
numpy: 1.16.2
scipy: 1.2.1
pyarrow: None
xarray: None
IPython: 6.4.0
sphinx: 1.8.2
patsy: 0.5.0
dateutil: 2.7.3
pytz: 2018.5
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 3.0.2
openpyxl: None
xlrd: 1.1.0
xlwt: None
xlsxwriter: None
lxml: None
bs4: 4.7.1
html5lib: 1.0.1
sqlalchemy: None
pymysql: None
psycopg2: 2.7.7 (dt dec pq3 ext lo64)
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None

</details>
