Add test for null return on version_compare with bad operator

Author: David Stockton

ext/standard/tests/versioning/version_compare_invalid_operator.phpt

@@ -0,0 +1,12 @@
+--TEST--
+Ensures null is returned if versions are compared with invalid operator
+--CREDITS--
+David Stockton - <[email protected]> - i3logix PHP Testfest 2017
+--SKIPIF--
+
+--FILE--
+<?php
+var_dump(version_compare('1.2', '2.1', '??'));
+?>
+--EXPECT--
+NULL