Check for egl->gbm before trying to use. am: 132d6485b1

Original change: https://android-review.googlesource.com/c/platform/external/virglrenderer/+/2975231

Change-Id: I86db68fbeb8ab14a235f746d173e9c4c9adf9534
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>