acquire global mixer-mutex instead of playHandlesMutex as we get deadlocks with monophonic instruments otherwise

git-svn-id: https://lmms.svn.sf.net/svnroot/lmms/trunk/lmms@509 0778d3d1-df1d-0410-868b-ea421aaaa00d

src/tracks/instrument_track.cpp

@@ -661,9 +661,9 @@ void instrumentTrack::processInEvent( const midiEvent & _me,
 				// for not modifying it's member variables
 				// asynchronously (while rendering!)
 				// which can result in segfaults
-				engine::getMixer()->lockPlayHandles();
+				engine::getMixer()->lock();
 				n->noteOff();
-				engine::getMixer()->unlockPlayHandles();
+				engine::getMixer()->unlock();
 				m_notes[_me.key()] = NULL;
 				emit noteDone( done_note );
 			}