We'd sometimes forget that the input was not originally a numeric.

Bug: v8:7135
Change-Id: I8bc690cc0c2dfac8a2a218ca56352b6a569825dc
Reviewed-on: https://chromium-review.googlesource.com/793039Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49667}