Fix more edge cases uncovered with tint:1781 Fixed: tint:1781 Change-Id: I58d120185f47c10bc9fe55dd95a198d496c4ec94 Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/113024 Reviewed-by: Antonio Maiorano <amaiorano@google.com> Kokoro: Kokoro <noreply+kokoro@google.com> Commit-Queue: Ben Clayton <bclayton@google.com> Auto-Submit: Ben Clayton <bclayton@google.com>