[native] Don't crash if TagInput is unmounted before error received

Summary:
I saw a bug where if I added a user, then left the screen before the server response came in, BUT the server response was an error, I would get a crash with "tagInput should be set".

The issue is that we have an invariant that assumes the TagInput is mounted when the error comes in. But if the user leaves the screen before the error, then the TagInput might be unmounted before the error.

Test Plan: Confirm there are no remaining instances of tagInput should be set in the codebase

Reviewers: atul, ginsu, tomek

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D7708