NotePlayHandle: send correct MidiNoteOff events if base note changed

When changing an InstrumentTrack's base note while NotePlayHandles are
active, they will send a wrong MidiNoteOff event due to the masterKey()
translation in InstrumentTrack::processOutEvent().

Therefore in NotePlayHandle remember the original base note value and
add the difference between original and current base note to the value
returned by NotePlayHandle::key(). Fixes hanging notes in MIDI-based
instruments such as ZynAddSubFX.

Furthermore some coding style improvements.

Closes #3146975.
(cherry picked from commit a9717c0cc3)

plugins/sf2_player/sf2_player.cpp

@@ -613,7 +613,7 @@ void sf2Instrument::playNote( notePlayHandle * _n, sampleFrame * )
 		}
 
 		fluid_synth_noteon( m_synth, m_channel, midiNote,
-							_n->getMidiVelocity() );
+							_n->midiVelocity() );
 
 		// get new voice and save it
 		fluid_synth_get_voicelist( m_synth, voices, poly, -1 );