winealsa.drv: check for alsa-lib return codes properly

[Timofei V. Bondarenko]

This patch fixes 2 generic bug in handling alsa-lib error codes returned
by snd_pcm_avail_update() function:
1) a signed return value (of type snd_pcm_sframes_t) assigned to 
unsigned DWORD variable and then compared to < 0
2) the return value translated by snd_pcm_frames_to_bytes() and then 
compared to (DWORD)-1

Neither way can catch usual overrun error (return value of -22).
More over in case of XRUN winealsa goes into near to infinite
transfer of (DWORD)-22 frames...

Regards,
	Tim.
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