Fix search with database prefix

wrap() only adds a table prefix when referencing a column with a table
name (such as `foo.bar`) - when only a single identifier is provided, it
is assumed to be a column name, which does not need a prefix.

Fixes #1659.

src/Discussion/Search/Gambit/FulltextGambit.php

@@ -53,7 +53,7 @@ public function apply(AbstractSearch $search, $bit)
         $query
             ->addSelect('posts_ft.most_relevant_post_id')
             ->join(
-                new Expression('('.$subquery->toSql().') '.$grammar->wrap('posts_ft')),
+                new Expression('('.$subquery->toSql().') '.$grammar->wrapTable('posts_ft')),
                 'posts_ft.discussion_id', '=', 'discussions.id'
             )
             ->addBinding($subquery->getBindings(), 'join')