Follow-up to #13452, fixing broken `uri.nil?` test.
Also remove the separate check for `uri` presence, as that would result
in a “Please review 2 errors below” while only one would be listed.
* Addition of update activity distribution by alias, minor correction
* Distribute Update activity after adding alias
* Add uniqueness verification to alias uri
* accept acct starting with @
* fix double-quoted to single-quoted
ThibG