Fixed typo in sql/log_event_server.cc related to ddl xid's.

This could only cause an issue if we got a crash at the very end of a
DDL log execution of an ALTER TABLE. The possible effect would be that
we would get two ALTER TABLE events in the binary log.

sql/log_event_server.cc

@@ -1299,7 +1299,7 @@ bool Query_log_event::write()
   if (thd && thd->binlog_xid)
   {
     *start++= Q_XID;
-    int8store(start, thd->query_id);
+    int8store(start, thd->binlog_xid);
     start+= 8;
   }