Allow ScreenSelectProfile to Finish() with guest players

Passing a -3 as profile index to ScreenSelectProfile's SetProfileIndex now
allows a player to play without having a local or USB profile assigned.

Also adds a message (PlayerProfileSet) that's broadcast anytime a player selects
a profile or chooses to play as a guest and subscribes ScreenSelectMusic to it.

src/ScreenSelectMusic.cpp

@@ -137,6 +137,7 @@ void ScreenSelectMusic::Init()
 	ScreenWithMenuElements::Init();
 
 	this->SubscribeToMessage( Message_PlayerJoined );
+	this->SubscribeToMessage( Message_PlayerProfileSet );
 
 	// Cache these values
 	// Marking for change -- Midiman (why? -aj)