Update RegExp.prototype.exec so that it returns 'null' instead of 'undefined' in case argument doesn't match corresponding regular expression.

JerryScript-DCO-1.0-Signed-off-by: Ruben Ayrapetyan [email protected]

tests/jerry/regexp-routines.js

@@ -17,7 +17,7 @@ var r;
 
 r = new RegExp ("a");
 assert (r.exec ("a") == "a");
-assert (r.exec ("b") == undefined);
+assert (r.exec ("b") == null);
 try {
 	r.exec.call({}, "a");
 	assert (false)