initialize m_currentValue, so we get deterministically wrong behavior if

Read() is never called (instead of leaving m_currentValue uninitialized)

stepmania/src/ThemeMetric.h

@@ -25,6 +25,7 @@ public:
 		m_sGroup( sGroup ),
 		m_sName( sName )
 	{
+		m_currentValue = T();
 		ThemeManager::Subscribe( this );
 	}