dialog: fix mem leak generated by missing replies

When cseq was to change generated replies, if those replies were never
generated (due to missing replies from UAC), the callback was leaking.

modules/dialog/dlg_handlers.c

@@ -909,6 +909,11 @@ static void dlg_seq_down_onreply_mod_cseq(struct cell* t, int type,
 	return;
 }
 
+static void free_final_cseq(void *cseq)
+{
+	shm_free(cseq);
+}
+
 static void fix_final_cseq(struct cell *t,int type,
 									struct tmcb_params *param)
 {
@@ -920,8 +925,6 @@ static void fix_final_cseq(struct cell *t,int type,
 	if (update_msg_cseq((struct sip_msg *)param->rpl,&cseq,0) != 0)
 		LM_ERR("failed to update CSEQ in msg\n");
 
-	shm_free(cseq.s);
-
 	return ;
 }
 
@@ -1686,7 +1689,7 @@ void dlg_onroute(struct sip_msg* req, str *route_params, void *param)
 
 			if ( d_tmb.register_tmcb( req, 0, TMCB_RESPONSE_FWDED,
 			fix_final_cseq,
-			(void*)final_cseq, 0)<0 ) {
+			(void*)final_cseq, free_final_cseq)<0 ) {
 				LM_ERR("failed to register TMCB (2)\n");
 			}
 		}