oggdec: Write to stdout instead of "-.wav" when reading from stdin and not output file name is given.
In bug #263762 it was reported that the behavior of oggdec was inconsistent
with its documentation: According to the man page, "oggdec" should write to
stdout, when reading its input from stdin and no output file name is given.
The "oggdec" executable writes to "-.wav" instead.
I adjusted the behavior of "oggdec" instead of adjusting the documentation
because it seems more sensible to write to stdout than to write to a file
called "-.wav". The code changes themselves are simple enough to be