(svn r1240) -Fix: OpenTTD once again compiles if ENABLE_NETWORK is disabled.

-Fix: removed some warnings
-Enabled ENABLE_NETWORK on windows again which I accidentally commented out.

network_udp.h

@@ -1,6 +1,8 @@
 #ifndef NETWORK_LAN_H
 #define NETWORK_LAN_H
 
+#ifdef ENABLE_NETWORK
+
 void NetworkUDPInitialize(void);
 bool NetworkUDPListen(SOCKET *udp, uint32 host, uint16 port, bool broadcast);
 void NetworkUDPReceive(SOCKET udp);
@@ -10,4 +12,6 @@ NetworkGameList *NetworkUDPQueryServer(const byte* host, unsigned short port);
 void NetworkUDPAdvertise(void);
 void NetworkUDPRemoveAdvertise(void);
 
+#endif
+
 #endif /* NETWORK_LAN_H */