This crash only happened on a compute test which following a render test.
This root case was that after the render test, mVertexArray11 became an
invalid pointer. However, compute test still went to the common path to
use mVertexArray11. mVertexArray11 is never updated since compute
shader doesn't need to triger DIRTY_BIT_VERTEX_ARRAY_BINDING.

This patch adds checking to avoid compute test to use mVertexArray11.
Besides, more ASSERT checking are added to convenient debugging.

Bug: angleproject:3518, angleproject:1663, angleproject:2619
Change-Id: I446214110d762fc259899cef7635f369fa1f59a7
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1652866Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jiajia Qin <jiajia.qin@intel.com>