When the multiplication steps fail, they have already thrown an
exception internally, so we should not throw another.
The power-of-two fast path erroneously did not throw at all for
a few input values.

Bug: chromium:818277
Change-Id: If90f6aa3e77fc72e3434daca3b898c77739933ab
Reviewed-on: https://chromium-review.googlesource.com/947254
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51711}