add test

ext/mysqli/tests/bug38003.phpt

@@ -0,0 +1,20 @@
+--TEST--
+Bug #38003 (in classes inherited from MySQLi it's possible to call private constructors from invalid context)
+--SKIPIF--
+<?php if (!extension_loaded("mysqli")) print "skip"; ?>
+--FILE--
+<?php
+
+class DB extends mysqli {
+
+    private function __construct($hostname, $username, $password, $database) {
+        var_dump("DB::__construct() called");
+    }
+}
+
+$DB = new DB();
+
+echo "Done\n";
+?>
+--EXPECTF--	
+Fatal error: Call to private DB::__construct() from invalid context in %s on line %d