fix musescore#15047: use the internal MuseSamplerWrapper position

since we're not working with the position from AbstractEventSequencer
(AbstractEventSequencer::eventsToBePlayed isn't called, so we don't update it)

src/framework/musesampler/internal/musesamplerwrapper.cpp

@@ -251,7 +251,7 @@ void MuseSamplerWrapper::updateRenderingMode(const audio::RenderMode mode)
 
 msecs_t MuseSamplerWrapper::playbackPosition() const
 {
-    return m_sequencer.playbackPosition();
+    return samplesToMsecs(m_currentPosition, m_sampleRate);
 }
 
 void MuseSamplerWrapper::setPlaybackPosition(const audio::msecs_t newPosition)