Avoid copying the last character to a local variable, by checking the parsing
state in a different order.

BUG=v8:7926

Change-Id: Ifb722dd3864737dc66d8e0885adbeba1376a059e
Reviewed-on: https://chromium-review.googlesource.com/1148569Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Florian Sattler <sattlerf@google.com>
Cr-Commit-Position: refs/heads/master@{#54680}