After putting up a solution for fixing @ mentioning in pending GENESIS sidebars in D10956, as a sanity check I wanted to check other places where we have pending threads and see if these also have issues when using the @ mentioning feature. I'm glad I did, because I also found an issue when creating a new standard pending GENESIS chat and using the @ mentioning would cause the app to crash.
{F1117908}
The cause of the crash was the same as in D10956 where we were attempting to get the chat mention search index from the `communityThreadIDForGenesisThreads`, but since this new pending thread wasn't resolved yet, it is not part of `communityThreadIDForGenesisThreads` so we were returning an `chatSearchIndex` as `undefined` even though in `useMentionTypeaheadChatSuggestions` we guarantee that there is a value there.
Since a pending standard GENESIS chat shouldn't have any resolved sidebars or subchannels, we really shouldn't be returning anything from `useMentionTypeaheadChatSuggestions` in the first place. So a solution that made sense to me here was to type the `chatSearchIndex` parameter as optional and have a check where if the `chatSearchIndex` is not set we just return the blank array that we initialized in the beginning as our list of `MentionTypeaheadChatSuggestionItem`s.
Depends on D10956