This avoids a DCHECK failure if we continue using the Assembler after
code generation abortion. Even though it might not be the best style to
still call methods on the Assembler after abortion, it's not a problem
apart from the firing DCHECK, so we apply this simple fix instead of
making sure to really abort everything immediately.

R=leszeks@chromium.org

Bug: chromium:1228720, chromium:1217074
Change-Id: Iac3a652f21e34534dd28fb1ab580ab2ee6df06dd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3024157Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75716}