[5.8] Fix DELETE queries with joins on PostgreSQL

[staudenmeir]

On PostgreSQL, Laravel implements DELETE queries with joins by adding their constraints after the WHERE constraints. If a query only has joins, the constraints aren't compiled:

DB::table('comments')
    ->join('posts', function ($join) {
        $join->on('posts.id', '=', 'comments.post_id')
            ->where('posts.active', 0);
    })
    ->delete();

# expected
delete from "comments" USING "posts"
where "posts"."id" = "comments"."post_id" and "posts"."active" = 0

# actual
delete from "comments" USING "posts"