Fixed post deletion

When post was deleted foreign keys in corresponding comments weren't NULLified.

src/Controllers/PostController.php

@@ -457,6 +457,11 @@ class PostController
 		if (InputHelper::get('submit'))
 		{
 			//remove stuff from auxiliary tables
+			foreach ($post->ownComment as $comment)
+			{
+				$comment->post = null;
+				R::store($comment);
+			}
 			$post->ownFavoritee = [];
 			$post->sharedTag = [];
 			R::store($post);

src/Models/Model_Comment_QueryBuilder.php

@@ -3,7 +3,11 @@ class Model_Comment_QueryBuilder implements AbstractQueryBuilder
 {
 	public static function build($dbQuery, $query)
 	{
-		$dbQuery->from('comment');
-		$dbQuery->orderBy('id')->desc();
+		$dbQuery
+			->from('comment')
+			->where('post_id')
+			->is()->not('NULL')
+			->orderBy('id')
+			->desc();
 	}
 }