Fix Level and Preferred Sorts to account for a song being in multiple sections

This commit properly returns you to the correct pack when leaving a folder or returning from another screen.
This is achieved by returning you to your last open section. Previously behavior searched for the first instance of the song in your sort and put you in that section.

src/GameState.cpp

@@ -175,7 +175,7 @@ GameState::GameState() :
 	m_Environment = new LuaTable;
 
 	m_bDopefish = false;
-
+	sLastOpenSection = "";
 	sExpandedSectionName = "";
 
 	// Don't reset yet; let the first screen do it, so we can use PREFSMAN and THEME.