We aren't properly handling them, were already firing UNIMPLEMENTED,
but can't continue with the loop.  Will follow up with real support.

Test: MEC capture of Manhattan on Windows
Bug: angleproject:3662
Change-Id: I7b77350b39971fda702eac8b19c6f29f36f78146
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2171759Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Cody Northrop <cnorthrop@google.com>