pc audio buffer bug

[rsc@research.att.com rsc@research.att.com]

There is a small bug in the buffer handling
in the PC devaudio (Soundblaster) driver.
Basically, if you open /dev/audio for writing,
partially fill a buffer, and then close /dev/audio,
the buffer doesn't get played.  You notice this
with smallish sound files, because nothing gets
played at all when the sound file is less than one
buffer in size.

My fix is to add 
	int omode;
	Buf *b;

at the beginning of 
/sys/src/9/pc/devaudio.c:/^audioclose
and in the case Qaudio that follows, insert
	omode = audio.amode;
before audio.amode = Aclosed;

Then, before the while(audio.active), insert
	if(omode == Awrite && audio.filling != 0) {
		print("flush...");
		b = audio.filling;
		audio.filling = 0;
		memset(b->virt+audio.curcount, 0, Bufsize-audio.curcount);
		swab(b->virt);
		putbuf(&audio.full, b);
		pokeaudio();
	}

I would post a diff, but I've hacked up devaudio.c
too much.  Just looking at the code for other 
architectures, it appears that next/devaudio.c also
suffers from this bug, while indigo3k/devaudio.c
does not.

Russ