add test for str(pysam.FastqProxy()) segfault

[graingert]

No description provided.

[graingert]

here's a demo on ubuntu: https://github.com/graingert/pysam-segfault

Step 7/7 : RUN ~/.virtualenvs/pysam/bin/python -c "str(__import__('pysam').FastqProxy())"
 ---> Running in d8adac336dd5
Segmentation fault (core dumped)
The command '/bin/sh -c ~/.virtualenvs/pysam/bin/python -c "str(__import__('pysam').FastqProxy())"' returned a non-zero code: 139

[AndreasHeger]

Thanks, FastqProxy now raises ValueError if instantiated directly.