If results.webkit.org is missing the record of a commit, we should fall-back to tip of tree when ews-build.webkit.org is comparing results.
<rdar://problem/103538068>
Pull request: https://github.com/WebKit/WebKit/pull/7890
Committed 258167@main (fc82999ee0dd): <https://commits.webkit.org/258167@main> Reviewed commits have been landed. Closing PR #7890 and removing active labels.