src/sndfile.hh: initialize all member variables

Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
programs/sndfile-play.c : Fix usage of HAVE_SNDIO_H.

The CMake build system will set this value to either 0 or 1 so the check
should not be for whether it is defined.
WIP
WIP