zero dest_id is pretty legal

Author: kelvich

src/pglogical_apply.c

@@ -854,6 +854,7 @@ mtm_send_reply(TransactionId xid, int node_id, MtmMessageCode msg_code)
 	MtmLock(LW_SHARED);
 	dest_id = Mtm->dmq_dest_ids[node_id - 1];
 	MtmUnlock();
+	Assert(dest_id >= 0);
 
 	MtmInitMessage(&msg, msg_code);
 	msg.dxid = xid;

src/resolver.c

@@ -408,7 +408,7 @@ scatter_status_requests(MtmConfig *mtm_cfg)
 				MtmLock(LW_SHARED);
 				dest_id = Mtm->dmq_dest_ids[node_id - 1];
 				MtmUnlock();
-				Assert(dest_id > 0);
+				Assert(dest_id >= 0);
 
 				dmq_push_buffer(dest_id, "txreq", &msg,
 								sizeof(MtmArbiterMessage));

src/state.c

@@ -983,7 +983,7 @@ check_status_requests(MtmConfig *mtm_cfg)
 		MtmLock(LW_SHARED);
 		dest_id = Mtm->dmq_dest_ids[sender_node_id - 1];
 		MtmUnlock();
-		Assert(dest_id > 0);
+		Assert(dest_id >= 0);
 
 		// XXX: and define channels as strings too
 		dmq_push_buffer(dest_id, "txresp", msg,