For an munderover tag, we try to access children[2] but only check whether there are at least 2 children.
<rdar://problem/83571752>
Created attachment 439355 [details] Patch
Committed r283127 (242185@main): <https://commits.webkit.org/242185@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 439355 [details].