Make sure we don't read out of bounds
Pull request: https://github.com/WebKit/WebKit/pull/10475
rdar://105728219
Committed 260649@main (ce8d9c65b8dd): <https://commits.webkit.org/260649@main> Reviewed commits have been landed. Closing PR #10475 and removing active labels.
<rdar://problem/105756671>