Fix issues #6383 and #4410 (pause issues). (#6590)

Fixes #6383 and fixes #4410.

Co-authored-by: Hyunjin Song <tteu.ingog@gmail.com>

src/core/Song.cpp

@@ -620,6 +620,7 @@ void Song::togglePause()
 	{
 		m_playing = false;
 		m_paused = true;
+		Engine::audioEngine()->clear();
 	}
 
 	m_vstSyncController.setPlaybackState( m_playing );

src/gui/editors/PianoRoll.cpp

@@ -858,8 +858,7 @@ void PianoRoll::setCurrentMidiClip( MidiClip* newMidiClip )
 	}
 
 	// force the song-editor to stop playing if it played a MIDI clip before
-	if( Engine::getSong()->isPlaying() &&
-		Engine::getSong()->playMode() == Song::Mode_PlayMidiClip )
+	if (Engine::getSong()->playMode() == Song::Mode_PlayMidiClip)
 	{
 		Engine::getSong()->playMidiClip( nullptr );
 	}