Add test for date_time_immutable invalid arguments

Author: mbniebergall

ext/date/tests/date_time_immutable001.phpt

@@ -0,0 +1,10 @@
+--TEST--
+DateTimeImmutable - invalid arguments
+--CREDITS--
+Mark Niebergall [email protected] UPHPU TestFest 2017
+--FILE--
+<?php
+var_dump(date_create_immutable('Invalid'));
+?>
+--EXPECTF--
+bool(false)