Fix conditions for updating element array buffer. It was skipping elementArrayBufferOverride->onReadResource() if mCurrentElementArrayBufferResource was null. BUG=angleproject:2389 Change-Id: If33a11d35225daf572796abc8c18f6d6df758b48 Reviewed-on: https://chromium-review.googlesource.com/989408 Commit-Queue: Frank Henigman <fjhenigman@chromium.org> Reviewed-by: Luc Ferron <lucferron@chromium.org>