Add extra checking to SendSyncResult::succeeded so we don't unwrap invalid SendSyncResult replies.
rdar://111895837
Pull request: https://github.com/WebKit/WebKit/pull/15901
Committed 266147@main (5d3f12cc83da): <https://commits.webkit.org/266147@main> Reviewed commits have been landed. Closing PR #15901 and removing active labels.