Fix stale validation cache on buffer deletion. When we would delete the currently bound element array buffer we would neglect to invalidate a specific validation cache variable. This incorrectly would let us skip buffer size validation and lead to internal invalid memory accesses. Bug: chromium:1105202 Change-Id: I23ab28ccd3ac6b5d461cb8745b930f4d42d53b35 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2298145 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>