When a liftoff function bails out after generating some constant pool,
this avoids to trigger a check in the Assembler destructor.

Bug: v8:6600

Change-Id: I79c595605bc0add1f3f5617ac7feedf162081d8a
Reviewed-on: https://chromium-review.googlesource.com/1026647Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Vincent Belliard <vincent.belliard@arm.com>
Cr-Commit-Position: refs/heads/master@{#52815}