Import upstreaam code to fix nll pointer dereference

[madpilot]

Summary

While using calibre I was experiencing frequent crashes. Some investigation leaded me to this upstream commit:

https://github.com/annulen/webkit/commit/0e75f3272d149bc64899c161f150eb341a2417af

I am running with this patch applied and I don't see crashes anymore.

I'd like to apply it to the official port.

I think this should also be merged to the quarterly branch.

Test Plan

I'm using patched code locally without problems. It's also alreaady committed to the upstream repo.

[tcberner]

If it builds, go ahead.
But please add the URL to the commit to the top of the patch so we have the content.