This uses the "null" buffer in the Renderer to bind an empty
buffer handle so ANGLE can maintain a consistent state.

Bug: chromium:1086532
Change-Id: I1912a1d1cb64433a285fcfced80a675619690a0b
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2219140
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>