Don't call `#uniq` on a relation

When there was no project, no search, and no current user or author
param, the AutocompleteController would call `#uniq!` on a relation
instead of an array. This performed the less-efficient `SELECT DISTINCT`
when it wasn't even needed (because the query wouldn't return duplicates
anyway - duplicates were only added by putting a user on top of the
list).

app/controllers/autocomplete_controller.rb

@@ -18,15 +18,14 @@ class AutocompleteController < ApplicationController
     if params[:search].blank?
       # Include current user if available to filter by "Me"
       if params[:current_user].present? && current_user
+        @users = @users.where.not(id: current_user.id)
         @users = [current_user, *@users]
       end
 
       if params[:author_id].present?
         author = User.find_by_id(params[:author_id])
-        @users = [author, *@users] if author
+        @users = [author, *@users].uniq if author
       end
-
-      @users.uniq!
     end
 
     render json: @users, only: [:name, :username, :id], methods: [:avatar_url]