oss: Add numid check in ctl plugin
oss: Add numid check in ctl plugin

Added the check of non-zero numid to optimize the look-up for the
element.

Signed-off-by: Takashi Iwai <4596b3305151c7ee743192a95d394341e3d3b644@suse.de>

Themaister/alsa-plugins-rsound,Distrotech/alsa-plugins,Distrotech/alsa-plugins,Distrotech/alsa-plugins