validate_program was not returning 0 for invalid programs that did not contain diagnostics with a severity greater than error.
This lead to broken behavior in logic that used the program.
Bug: chromium:1392853
Change-Id: Id860e266cfe24ade955edf4f2f2a9c26c2e117fa
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/112560
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@chromium.org>