Fix introduced warning

tests/test-mstring.c

@@ -80,6 +80,7 @@ static void test_utf8_it(void)
   string_it_t it2;
 
   string_init(s);
+  string_it_end(it2, s);
 
   for(string_it(it, s) ; !string_end_p(it); string_next(it)) {
     assert(0); // Shall not be called