alsa: suppress stderr noise from device probing

[youssefadly237]

uncomments AlsaErrorHandler with proper init/term lifecycle, fixes dangling pointer on dlclose (regressed in 96b86da)

Ppreviously the unregister was missing, causing SIGSEGV on dynamic unload

noise example

ALSA lib pcm_dsnoop.c:572:(snd_pcm_dsnoop_open) [error.pcm] unable to open slave
ALSA lib pcm_dmix.c:1000:(snd_pcm_dmix_open) [error.pcm] unable to open slave
ALSA lib pcm.c:2722:(snd_pcm_open_noupdate) [error.pcm] Unknown PCM cards.pcm.rear
ALSA lib pcm.c:2722:(snd_pcm_open_noupdate) [error.pcm] Unknown PCM cards.pcm.center_lfe
ALSA lib pcm.c:2722:(snd_pcm_open_noupdate) [error.pcm] Unknown PCM cards.pcm.side
Cannot connect to server socket err = No such file or directory
Cannot connect to server request channel
jack server is not running or cannot be started
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock
Cannot connect to server socket err = No such file or directory
Cannot connect to server request channel
jack server is not running or cannot be started
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock
ALSA lib pcm_oss.c:404:(_snd_pcm_oss_open) [error.] Cannot open device /dev/dsp
ALSA lib pcm_oss.c:404:(_snd_pcm_oss_open) [error.] Cannot open device /dev/dsp
ALSA lib pcm_a52.c:1036:(_snd_pcm_a52_open) [error.] a52 is only for playback
ALSA lib confmisc.c:160:(snd_config_get_card) [error.core] Invalid field card
ALSA lib pcm_usb_stream.c:481:(_snd_pcm_usb_stream_open) [error.] Invalid card 'card'
ALSA lib confmisc.c:160:(snd_config_get_card) [error.core] Invalid field card
ALSA lib pcm_usb_stream.c:481:(_snd_pcm_usb_stream_open) [error.] Invalid card 'card'
ALSA lib pcm_dmix.c:1000:(snd_pcm_dmix_open) [error.pcm] unable to open slave
Cannot connect to server socket err = No such file or directory
Cannot connect to server request channel
jack server is not running or cannot be started
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock

closes #163