Fixes Vulkan validation-layer errors. Found by dEQP tests that
use small viewports and/or scissors (see Buganizer bugs for
details).
Bug: angleproject:4431
Bug: b/157933235
Bug: b/157933198
Change-Id: I83966906d70c30a4b50209cf1a33649bf69e3dd8
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2225607
Commit-Queue: Ian Elliott <ianelliott@google.com>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
