gprs: Add assertion for msg != NULL to bssgp_msgb_alloc (Coverity)

Currently out-of-memory is not handled by bssgp_msgb_alloc, leading
to SEGV failures if msgb_alloc_headroom returns NULL.

This commit adds an OSMO_ASSERT to catch this case, which improves
the situation only slightly. But bssgp_msgb_alloc is used in many
places without checking the return value, so just adding a
conditional early NULL return would not fix the issue either.

Fixes: Coverity CID 1293377
Sponsored-by: On-Waves ehf
1 file changed