Log Message:
Fixes for SpiralSound/Midi.C

* test for failure of open() should be == -1, not == 0
	This causes Open() to behave as intended, only creating the
	m_MidiReader thread if the MIDI device is successfully opened.

* unconditionally initialize m_Mutex in Open()

* conditionally close m_MidiReader in Close(), if NULL do nothing

* make m_MidiFd and m_MidiWrFd the same file descriptor.  The MIDI
	device special file can only be opened once at a time.