The texture cache could become out of sync. And we could end up
dereferencing an invalid pointer.

Bug: chromium:943538
Change-Id: I6a99a04e80fc551b6177e25b7bee09c6ae226340
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1541718Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>