Clear serverlistultimatecount when leaving Server Browser for any reason

This is the easiest existing tracked variable to ensure matches 1:1 to "you are joining a netgame from the Server Browser".

src/d_main.c

@@ -987,6 +987,7 @@ void D_ClearState(void)
 	// (otherwise the game still thinks we're playing!)
 	SV_StopServer();
 	SV_ResetServer();
+	serverlistultimatecount = 0;
 
 	for (i = 0; i < MAXPLAYERS; i++)
 		CL_ClearPlayer(i);

src/menus/play-online-server-browser.c

@@ -13,6 +13,13 @@
 void M_ServerListFillDebug(void);
 #endif
 
+// Quit
+static boolean M_ServerBrowserQuit(void)
+{
+	serverlistultimatecount = 0;
+	return true;
+}
+
 menuitem_t PLAY_MP_ServerBrowser[] =
 {
 
@@ -38,7 +45,7 @@ menu_t PLAY_MP_ServerBrowserDef = {
 	M_DrawMPServerBrowser,
 	M_MPServerBrowserTick,
 	NULL,
-	NULL,
+	M_ServerBrowserQuit,
 	M_ServerBrowserInputs
 };