Added semi-workaround method for network thread shutdown:

Currently closing game while network thread is waiting for something is
very bug-prone, since network thread may resume during shutdown and
access partially destroyed client state.

Now if exit has been requested, the very first step would be semi-
graceful shutdown of network thread (via exception throwing). This may
in theory skip some cleanup in non-RAII code, but since game is shutting
down this does not matters much.

This logic applies to:
- shutting down while network thread is waiting for dialogs
- shuttind down while network thread waiting for animations in combat

client/ClientCommandManager.cpp

@@ -179,11 +179,6 @@ void ClientCommandManager::handleRedrawCommand()
 	GH.windows().totalRedraw();
 }
 
-void ClientCommandManager::handleNotDialogCommand()
-{
-	LOCPLINT->showingDialog->setn(false);
-}
-
 void ClientCommandManager::handleTranslateGameCommand()
 {
 	std::map<std::string, std::map<std::string, std::string>> textsByMod;
@@ -584,9 +579,6 @@ void ClientCommandManager::processCommand(const std::string & message, bool call
 	else if(commandName == "redraw")
 		handleRedrawCommand();
 
-	else if(commandName == "not dialog")
-		handleNotDialogCommand();
-
 	else if(message=="translate" || message=="translate game")
 		handleTranslateGameCommand();