Don't check set size on Windows.

socket is an opaque object on Windows, so this check isn't valid.

lib/mosquitto.c

@@ -831,9 +831,11 @@ int mosquitto_loop(struct mosquitto *mosq, int timeout, int max_packets)
 	int maxfd = 0;
 
 	if(!mosq || max_packets < 1) return MOSQ_ERR_INVAL;
+#ifndef WIN32
 	if(mosq->sock >= FD_SETSIZE || mosq->sockpairR >= FD_SETSIZE){
 		return MOSQ_ERR_INVAL;
 	}
+#endif
 
 	FD_ZERO(&readfds);
 	FD_ZERO(&writefds);