Windows MIDI driver improved

- Stop sending all MIDI messages to a worker thread to be played.
  Instead, call the event handler directly (with mutual exclusion).
  This simplifies the code and reduces latency.
- Move initialization before worker thread creation - without this,
  TiMidity++ might not be initialized before the 1st message arrives
  (I actually had this problems when using VMPK, which sends a bank &
  program change message immediately on startup)

Signed-off-by: TAMUKI Shoichi <tamuki@linet.gr.jp>