If we encounter a global twice, the stack vector was not popped, which could trigger false cyclic-dependency errors. Because the cyclic dependency did not actually exist, later logic could break, expecting to find a global->global edge which did not exist.
Fixed: chromium:1273451
Change-Id: I9d99f1aeeaea042d9ed847a878c4717803122240
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/70980
Reviewed-by: David Neto <dneto@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
91785d277b