Fix validate state cache after XFB buffer deleted. Bug: chromium:1317650 Change-Id: Iec9f1167c3b2957091dd0f4ef3efcfcd7c4bf3c0 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3594250 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Auto-Submit: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>