If we don't have anything committed, the branch_point should be HEAD. Additionally, computing the branch_point is relatively expensive, we can avoid this computation when we're rebasing because we know that the branch point is the tip of the branch we're rebasing on.
<rdar://problem/96080523>
Pull request: https://github.com/WebKit/WebKit/pull/1861
Committed 251934@main (b571cde426fc): <https://commits.webkit.org/251934@main> Reviewed commits have been landed. Closing PR #1861 and removing active labels.