Segfault calling ohlc on column-wise groupby 
#### Code Sample, a copy-pastable example if possible

```python
y = pd.DataFrame([1,2])
y.groupby(y.columns, axis=1).ohlc()
```
causes
```
Segmentation fault: 11
```

#### Problem description

Calling ohlc after column-wise groupby on a dataframe with more than one row causes a segfault. 

#### Expected Output

Not a segfault. Probably something like:

```
     0
  open high low close
0    1    2   1     2
```

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

<details>

------------------
commit: None
python: 3.6.5.final.0
python-bits: 64
OS: Darwin
OS-release: 15.6.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.22.0
pytest: None
pip: 9.0.3
setuptools: 39.0.1
Cython: None
numpy: 1.14.2
scipy: None
pyarrow: None
xarray: None
IPython: 6.3.0
sphinx: None
patsy: None
dateutil: 2.7.2
pytz: 2018.3
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 2.2.2
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: 1.0.1
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None

</details>
