Previously was relying on whether `SaveReplay` returns null, but since
I've changed it to use the standard "prepare score for import" path, the
button has to check for local availability after import since that path
doesn't return null on fail.
Not sure on the future of this, but given it is used in the
save-failed-reply pull request (#18785) I think it's fine to add back
for now.
Without this, JSON parsing of older scores in server-side storage will
fail on missing enum type.
Really this shouldn't happen but I managed to make it happen. Until this
comes up again in a way that matters, let's just fix the LINQ crash from
`SingleOrDefault`.
I've tested this to work as expected in the broken scenario.