Since tokens turn illegal automatically upon failure, we can delay checking in
places where we'll return upon illegal token anyway. We still need checks
before uses of a possible invalid expression (nullptr in parser), so keep those
checks for now; possibly pushing a previously higher check to right before the
dereference.

Bug: v8:8363 ,v8:7926

Change-Id: Ia402fc83c15f4c3258a335614b9213f8211a3c53
Reviewed-on: https://chromium-review.googlesource.com/c/1299081Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56985}