merge_pr_53319

Fix token pasting with empty fallbacks.

When deciding whether we'd need to insert a dummy comment between
two tokens in CSS token pasting, an empty fallback could confuse
the logic, in that we thought we inserted an EOF token.

Fix by having an early return from empty fallbacks; they shouldn't
affect the output in any reasonable way.

Fixed: 426549962
Change-Id: I0d1f330dd5a507c660395e0d7089873fa5382d12
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6650923
Auto-Submit: Steinar H Gunderson sesse@chromium.org
Commit-Queue: Anders Hartvoll Ruud andruud@chromium.org
Reviewed-by: Anders Hartvoll Ruud andruud@chromium.org
Cr-Commit-Position: refs/heads/main@{#1477216}