fix insert before

src/NodeManipulator/ClassInsertManipulator.php

@@ -59,7 +59,7 @@ public function addPropertyToClass(Class_ $class, string $name, ?Type $type): vo
      */
     private function insertBefore(array $stmts, Stmt $stmt, int $key): array
     {
-        array_splice($stmts, $key, 0, [$stmt]);
+        array_splice($stmts, max(0, $key - 1), 0, [$stmt]);
 
         return $stmts;
     }