vrend: Don't try to deref gbm if it was not initialized

minigbm allocations being enabled does not imply that GBM is also initialized, e.g. if the renderer uses a GLX context, so don't try to dereference gbm.

added bugfix label

requested review from @jbates

assigned to @gerddie

r-b

added 3 commits

• e2f3c2c9...138b8ad9 - 2 commits from branch virgl:master
• edf38395 - vrend: Don't try to deref gbm if it was not initialized

Compare with previous version

enabled an automatic merge when the pipeline for edf38395 succeeds

merged