Fix error collection on Song instead of MainWindow

plugins/audio_file_processor/audio_file_processor.cpp

@@ -34,6 +34,7 @@
 #include "audio_file_processor.h"
 #include "Engine.h"
 #include "Song.h"
+#include "MainWindow.h"
 #include "InstrumentTrack.h"
 #include "NotePlayHandle.h"
 #include "interpolation.h"
@@ -240,7 +241,7 @@ void audioFileProcessor::loadSettings( const QDomElement & _this )
 		{
 			QString message = tr( "Sample not found: %1" ).arg( m_sampleBuffer.audioFile() );
 
-			Engine::getSong()->collectError( message );
+			Engine::mainWindow()->collectError( message );
 		}
 	}
 	else if( _this.attribute( "sampledata" ) != "" )