Disable opening cheats window in MP

When connecting to a server, also reset cheats.

This should fix #2811

data/language/english_uk.txt

@@ -4017,6 +4017,7 @@ STR_5712    :Can't modify permission that you do not have yourself
 STR_5713    :Kick Player
 STR_5714    :Show options window
 STR_5715    :New Game
+STR_5716    :Not allowed in multiplayer mode
 
 #############
 # Scenarios #

src/localisation/string_ids.h

@@ -2308,6 +2308,8 @@ enum {
 	
 	STR_NEW_GAME = 5715,
 
+	STR_NOT_ALLOWED_IN_MULTIPLAYER = 5716,
+
 	// Have to include resource strings (from scenarios and objects) for the time being now that language is partially working
 	STR_COUNT = 32768
 };

src/network/network.cpp

@@ -48,6 +48,7 @@ extern "C" {
 #include "../scenario.h"
 #include "../windows/error.h"
 #include "../util/util.h"
+#include "../cheats.h"
 }
 
 #pragma comment(lib, "Ws2_32.lib")
@@ -665,6 +666,7 @@ bool Network::BeginServer(unsigned short port, const char* address)
 		return false;
 	}
 
+	cheats_reset();
 	LoadGroups();
 
 	NetworkPlayer* player = AddPlayer();
@@ -852,6 +854,7 @@ void Network::UpdateClient()
 			if (error == 0) {
 				status = NETWORK_STATUS_CONNECTED;
 				server_connection.ResetLastPacketTime();
+				cheats_reset();
 				Client_Send_AUTH(gConfigNetwork.player_name, "");
 				window_network_status_open("Authenticating...");
 			}

src/windows/cheats.c

@@ -36,6 +36,7 @@
 #include "../world/scenery.h"
 #include "../interface/themes.h"
 #include "../cheats.h"
+#include "../network/network.h"
 #include "error.h"
 
 #define CHEATS_MONEY_INCREMENT MONEY(5000,00)
@@ -760,6 +761,13 @@ static void cheat_set_staff_speed(uint8 value)
 
 void window_cheats_open()
 {
+#ifndef DISABLE_NETWORK
+	if (network_get_mode() != NETWORK_MODE_NONE)
+	{
+		window_error_open(STR_WARNING_IN_CAPS, STR_NOT_ALLOWED_IN_MULTIPLAYER);
+		return;
+	}
+#endif
 	rct_window* window;
 
 	// Check if window is already open