The ReduceStringPrototypeStartsWith implementation in TurboFan
was doing the CheckString too late, after returning "false" in
case there are no arguments.

Fixed: chromium:1065741
Change-Id: I1016383d65120d3b050e76d6ac41986497af0b8d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2129639
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66948}