Vulkan: Fix transform feedback on AMD platform Make sure pCounterBufferOffsets is never a null pointer when counterBufferCount is greater than zero. Bug: angleproject:3206 Change-Id: If161473239b53d2a65b1cccaaf1426a4fefd243a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2152030 Commit-Queue: Mohan Maiya <m.maiya@samsung.com> Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>