Lock user out of menu when replay goes to intermission

- Access to the replay menu in intermission leads to
  various problems
  - Broken options
  - HOM effect
- You can press A on the intermission screen to end it

src/k_menufunc.c

@@ -668,6 +668,15 @@ menu_t *M_SpecificMenuRestore(menu_t *torestore)
 //
 void M_StartControlPanel(void)
 {
+	if (demo.playback && gamestate == GS_INTERMISSION)
+	{
+		// At this point the replay has ended.
+		// The only menu option that works is "Stop Playback".
+		// And intermission can be finished by pressing the
+		// A button, so having a menu at all is useless.
+		return;
+	}
+
 	INT32 i;
 
 	G_ResetAllDeviceGameKeyDown();

src/y_inter.cpp

@@ -2271,6 +2271,13 @@ void Y_StartIntermission(void)
 
 	G_SetGamestate(GS_INTERMISSION);
 
+	if (demo.playback)
+	{
+		// Replay menu is inacessible here.
+		// Press A to continue!
+		M_ClearMenus(true);
+	}
+
 	if (musiccountdown == 0)
 	{
 		Y_PlayIntermissionMusic();