[Python][C++] Segfault for dictionary_encode on empty chunked_array (edge case)

a reproducer is here :

import pyarrow as pa
aa = pa.chunked_array([pa.array(['a', 'b', 'c'])])
aa[:0].dictionary_encode()  
# Segmentation fault: 11

For pyarrow=0.14, I could not reproduce.
I use a conda version : "pyarrow 0.15.0 py37hdca360a_0 conda-forge"