Fix messagepack EXT parsing

When we read `ext` we actually do not get any object, so we MUST NOT
insert `parser->cur_obj` multiple times, as we will have use-after-free
on unref. This is a serious bug.

Issue: #303
Closes: #303

src/ucl_msgpack.c

@@ -1146,9 +1146,14 @@ ucl_msgpack_consume (struct ucl_parser *parser)
 
 
 			/* Insert value to the container and check if we have finished array */
-			if (!ucl_msgpack_insert_object (parser, NULL, 0,
+			if (parser->cur_obj) {
+				if (!ucl_msgpack_insert_object(parser, NULL, 0,
 					parser->cur_obj)) {
-				return false;
+					return false;
+				}
+			}
+			else {
+				/* We have parsed ext, ignore it */
 			}
 
 			if (ucl_msgpack_is_container_finished (container)) {
@@ -1634,5 +1639,7 @@ ucl_msgpack_parse_ignore (struct ucl_parser *parser,
 		return -1;
 	}
 
+	parser->cur_obj = NULL;
+
 	return len;
 }