Fix count query detection, the select array may not be zero based

src/foreignField/ForeignFieldQueryExtension.php

@@ -223,7 +223,7 @@ static private function enableJoin(ElementQuery $query, ForeignField $field) {
   static public function isCountQuery(ElementQuery $query) {
     return (
       count($query->select) == 1 &&
-      $query->select[0] == 'COUNT(*)'
+      reset($query->select) == 'COUNT(*)'
     );
   }
 }