Update enableMIDI (#2912)

MIDISampler has a different enableMIDI method from the one in MIDICallbackInstrument. This makes them more similar, and fixes the issue with MIDISampler not playing from AppleSequencer in Xcode 15.3.

Sources/AudioKit/MIDI/MIDISampler.swift

@@ -43,12 +43,16 @@ open class MIDISampler: AppleSampler, NamedNode {
  fatalError("Expected AU to respond to MIDI.")
  }
  CheckError(MIDIDestinationCreateWithBlock(midiClient, cfName, &midiIn) { packetList, _ in
- for e in packetList.pointee {
- for event in e {
- event.data.withUnsafeBufferPointer { ptr in
- guard let ptr = ptr.baseAddress else { return }
- midiBlock(AUEventSampleTimeImmediate, 0, event.data.count, ptr)
+ withUnsafePointer(to: packetList.pointee.packet) { packetPtr in
+ var p = packetPtr
+ for _ in 1...packetList.pointee.numPackets {
+ for event in p.pointee {
+ event.data.withUnsafeBufferPointer { ptr in
+ guard let ptr = ptr.baseAddress else { return }
+ midiBlock(AUEventSampleTimeImmediate, 0, event.data.count, ptr)
+ }
  }
+ p = UnsafePointer<MIDIPacket>(MIDIPacketNext(p))
  }
  }
  })