RegExp: treat undefined argument as empty.

new RegExp() and new RegExp(undefined) calls now results in the
same 'source' pattern.

JerryScript-DCO-1.0-Signed-off-by: Peter Gal pgal.u-szeged@partner.samsung.com

tests/jerry/regexp-construct.js

@@ -86,3 +86,15 @@ assert (r.ignoreCase == true);
 assert (r.multiline == true);
 
 assert(Object.prototype.toString.call(RegExp.prototype) === '[object RegExp]');
+
+
+/* The 'undefined' argument for the RegExp constructor should not be converted to string,
+ * and it should behave just like when there is no argument.
+ */
+r1 = new RegExp();
+r2 = new RegExp(undefined);
+var foo;
+r3 = new RegExp(foo)
+
+assert (r1.source === r2.source);
+assert (r2.source === r3.source);