The second argument of FromParameterIndex should be the parameter count, including the receiver.

Previously it worked by chance, because the code was trying to access the receiver but did not include it in the parameter count, accessing the first argument. This does not work anymore when the arguments are reversed (V8_REVERSE_JSARGS).

Change-Id: I8ca9054a99d074c130f9a9b444e7b8a379840991
Bug: v8:10201
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2282531Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68742}