We really want to catch such errors. (std::optional throws an
exception in some of these cases.)

Change-Id: I7f8c3aff38aed1b3cbe52bcfb92062268fd3b201
Reviewed-on: https://chromium-review.googlesource.com/1177387Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55158}