- refactored the exit calls out of the networking code

These ones were particularly bad examples of misusing the exit handlers by temporarily installing one themselves and then calling exit to clean stuff up.

Now they just return an error code to D_DoomMain to perform a regular exit.

src/d_net.cpp

@@ -1653,7 +1653,7 @@ static void SendSetup (uint32_t playersdetected[MAXNETNODES], uint8_t gotsetup[M
 // Works out player numbers among the net participants
 //
 
-void D_CheckNetGame (void)
+bool D_CheckNetGame (void)
 {
 	const char *v;
 	int i;
@@ -1674,8 +1674,13 @@ void D_CheckNetGame (void)
 			"\nIf the game is running well below expected speeds, use netmode 0 (P2P) instead.\n");
 	}
 
+	int result = I_InitNetwork ();
 	// I_InitNetwork sets doomcom and netgame
-	if (I_InitNetwork ())
+	if (result == -1)
+	{
+		return false;
+	}
+	else if (result > 0)
 	{
 		// For now, stop auto selecting PacketServer, as it's more likely to cause confusion.
 		//NetMode = NET_PacketServer;
@@ -1739,6 +1744,8 @@ void D_CheckNetGame (void)
 
 	if (!batchrun) Printf ("player %i of %i (%i nodes)\n",
 			consoleplayer+1, doomcom.numplayers, doomcom.numnodes);
+	
+	return true;
 }