Fix crash at WebCore::findWordBoundary
<rdar://122491165>
Committed 272448.1026@safari-7618-branch (99b865d3d529): <https://commits.webkit.org/272448.1026@safari-7618-branch> Reviewed commits have been landed. Closing PR #1267 and removing active labels.
Committed 279076@main (d8b017db8ea6): <https://commits.webkit.org/279076@main> Reviewed commits have been landed. Closing PR #28867 and removing active labels.