from: search prefix 500s when the supplied account cannot be found

[aescling]

see mastodon/mastodon#17941

importing here as my WIP commits keep spamming the issue upstream

[aescling]

945c9b1 strictly solves the issue and also changes behavior in ways i personally find preferable. it litters changes across the codebase and i don’t know if i like that

i think the way i raise errors to handle the problem is very sketch; i would like to better understand the control flow for text search so i can handle things in a more idiomatic- and cleaner-feeling way

i would like to see the search API capable of sending error responses; and i would like to see the front end not just throw them at the toast, probably displaying such errors in the search results column

[aescling]

mastodon/mastodon#17963