Fix having no last loaded filename for surfaces if no xml file found

Previously the mesh was copied every time `BaseSurface::getMesh()` was called.

src/Application/SettingsLoader.cpp

@@ -12,6 +12,10 @@ SettingsLoader * SettingsLoader::instance(){
 	return _instance;
 }
 
+SettingsLoader::SettingsLoader(){
+    _lastLoadedFilename = "surfaces.xml";
+}
+
 bool SettingsLoader::load(SurfaceStack & surfaces, MediaServer & mediaServer, string fileName){
 	
 	ofxXmlSettings * xmlSettings = new ofxXmlSettings();

src/Application/SettingsLoader.h

@@ -21,6 +21,8 @@ class SettingsLoader {
 	
 	private:
 		static SettingsLoader * _instance;
+    
+        SettingsLoader();
 	
 		BaseSurface * getTriangleSurface(ofxXmlSettings * xmlSettings);
 		BaseSurface * getQuadSurface(ofxXmlSettings * xmlSettings);