Log Message:
libao-sun: convert 24-bit samples to 32-bit samples

working around the inability of the netbsd 9 kernel (at least) to
handle 24-bit lpcm directly in its default configuration. this
fixes problems playing 24-bit flac in cmus, at least.

with the kernel compiled with AUDIO_SUPPORT_LINEAR24 this is not
actually necessary and we should maybe consider doing that by default.