The CHECK was checking that we return the exception sentinel if an
exception is pending. The other way is actually equally important: If we
return the exception sentinel, a pending exception must be scheduled.

Since the CEntry stub assumes that all values returned from runtime
functions are valid tagged values (pointing into the JS heap), do also
check that. This check would have prevented the linked issue.

Bug: chromium:1311960

R=jkummerow@chromium.org
CC=​cbruni@chromium.org

Change-Id: I833d2968529e3b73f3009e0104b46182197c2d23
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3675098Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81145}