The callback to AsyncStreamingProcessor::OnFinishedStream would
call into v8 internals without restoring the current context if
the processed module had no code. Instead, now always restore the
context before doing any finishing work.

Bug: chromium:915493
Change-Id: Ib779df81301ad1e3597515a4173c9a57efc593ac
Reviewed-on: https://chromium-review.googlesource.com/c/1397672Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Stephan Herhut <herhut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58612}