Reduce private member accesses

Reduce direct accesses to `m_simpleSerializingMode` by using
the method `isSimpleSerializing` and extending `setSimpleSerializing`
with a parameter.

include/Track.h

@@ -115,9 +115,9 @@ class LMMS_EXPORT Track : public Model, public JournallingObject
 	void saveSettings( QDomDocument & doc, QDomElement & element ) override;
 	void loadSettings( const QDomElement & element ) override;
 
-	void setSimpleSerializing()
+	void setSimpleSerializing(bool simpleSerializing = true)
 	{
-		m_simpleSerializingMode = true;
+		m_simpleSerializingMode = simpleSerializing;
 	}
 
 	// -- for usage by Clip only ---------------

src/core/Track.cpp

@@ -191,7 +191,7 @@ Track* Track::clone()
  */
 void Track::saveSettings( QDomDocument & doc, QDomElement & element )
 {
-	if( !m_simpleSerializingMode )
+	if (!isSimpleSerializing())
 	{
 		element.setTagName( "track" );
 	}
@@ -217,9 +217,9 @@ void Track::saveSettings( QDomDocument & doc, QDomElement & element )
 	element.appendChild( tsDe );
 	saveTrackSpecificSettings( doc, tsDe );
 
-	if( m_simpleSerializingMode )
+	if (isSimpleSerializing())
 	{
-		m_simpleSerializingMode = false;
+		setSimpleSerializing(false);
 		return;
 	}
 
@@ -267,7 +267,7 @@ void Track::loadSettings( const QDomElement & element )
 		setColor(QColor{element.attribute("color")});
 	}
 
-	if( m_simpleSerializingMode )
+	if (isSimpleSerializing())
 	{
 		QDomNode node = element.firstChild();
 		while( !node.isNull() )
@@ -279,7 +279,9 @@ void Track::loadSettings( const QDomElement & element )
 			}
 			node = node.nextSibling();
 		}
-		m_simpleSerializingMode = false;
+
+		setSimpleSerializing(false);
+
 		return;
 	}