Fix formatting error message (invalid table name) in handler tests.

sql/sql_handler.cc

@@ -550,7 +550,7 @@ mysql_ha_fix_cond_and_key(SQL_HANDLER *handler,
       if ((handler->keyno= find_type(keyname, &table->s->keynames, 1+2)-1)<0)
       {
         my_error(ER_KEY_DOES_NOT_EXITS, MYF(0), keyname,
-                 handler->handler_name);
+                 handler->handler_name.str);
         return 1;
       }
     }