Fix TLV dB parser in case of used container

Fix TLV dB parser in case of used container

In case when dB information does not appear as the only TLV type in the
stream (it might be wrapped in a container, but the container can not
have any other type), the TLV parser fails to get the dB TLV pointer.

This commit fixes it by distinguishing between TLV parse error and dB
information not being found in a container (-ENOENT), so the parser can iterate
over all elements in the container.

Also, it fixes out-of-bounds read in case of malicious TLV record.

Closes: https://github.com/alsa-project/alsa-lib/pull/409
Signed-off-by: Arkadiusz Bokowy <arkadiusz.bokowy@gmail.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>