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/+/2323644Reviewed-by: Jamie Madill <jmadill@chromium.org>