Move WaitEventSetWait after PQgetCopyData

pgxn/neon/libpagestore.c

@@ -1152,7 +1152,8 @@ pageserver_try_receive(shardno_t shard_no)
 
 	while (true)
 	{
-		if (PQisBusy(shard->conn))
+		rc = PQgetCopyData(shard->conn, &resp_buff.data, 1 /* async */);
+		if (rc == 0)
 		{
 			WaitEvent	event;
 			if (WaitEventSetWait(shard->wes_read, 0, &event, 1,
@@ -1161,10 +1162,6 @@ pageserver_try_receive(shardno_t shard_no)
 			{
 				return NULL;
 			}
-		}
-		rc = PQgetCopyData(shard->conn, &resp_buff.data, 1 /* async */);
-		if (rc == 0)
-		{
 			if (!PQconsumeInput(shard->conn))
 			{
 				return NULL;