allocateResource can fail if the device has been removed or there
is no more video memory. Hence, the return value needs to checked
for errors instead of simply asserting that the result doesn't equal
angle::Result::Stop.

Bug: chromium:1192771
Change-Id: I794f288f16917ef50e45f6f3ab60ee3ebc5941d9
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2787249Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Rafael Cintron <rafael.cintron@microsoft.com>