An empty PR number causes DetermineLabelOwner to error. Fix property retrieval and add error handling.
<rdar://problem/115447713>
Pull request: https://github.com/WebKit/WebKit/pull/17748
Committed 267966@main (79744779ccbb): <https://commits.webkit.org/267966@main> Reviewed commits have been landed. Closing PR #17748 and removing active labels.
Re-opening for pull request https://github.com/WebKit/WebKit/pull/17775