RemoteVstPlugin: fix build failure due to out-of-bounds-array-access-warning

Newer versions of GCC seem to assume an array size of 0 for arrays whose
size is not specified explicitely. This causes a warning about an
out-of-bounds array access.
InstrumentTrack: generally do not forward NoteOn/NoteOff/KeyPressure events

If we receive MidiNoteOn, MidiNoteOff or MidiKeyPressure events we always
kind of handle them in processInEvent() so do not forward them to the
instrument.

This fixes a freeze when loading VST plugins as PianoView::focusOutEvent()
tried to send MIDI events to the not yet completely loaded and thus locked
VST plugin.

Closes #160.