Fix null escape in character classes (#3192)

Fixes #3001.

JerryScript-DCO-1.0-Signed-off-by: Dániel Bátyai dbatyai@inf.u-szeged.hu

tests/jerry/regexp-character-class.js

@@ -133,3 +133,10 @@ assert (r == "abcdefghjklmnopqrstuvwxyz");
 r = new RegExp("[\\u0800-\\uffff]", "g");
 assert (r.test ("\uffff"));
 assert (!r.test ("\uffff"));
+
+r = new RegExp("[\0]");
+assert (r.test ("\0"));
+assert (!r.test ("0"));
+
+r = new RegExp("[\0-\1]");
+assert (r.test ("\1"));