Add patch to fix interpreter crash on HDF5 files with simple strings

Fixes crash when loading HDF5 files with simple strings in them.

The issue can be reproduced with:

apt install octave python3-h5py
python3 -c "import h5py, numpy; f = h5py.File('outfile.hdf5', 'w'); f.create_dataset('scan/date', data=numpy.string_('Mon Jun 18 03:34:30 2018')); f.close()"
octave-cli --eval "load outfile.hdf5"

• Debian bug report: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=959109
• Upstream bug report: https://savannah.gnu.org/bugs/index.php?58268
• Upstream patch: https://hg.savannah.gnu.org/hgweb/octave/rev/9646d752c76c

@sebastien