pcm_file: fix SEGFAULT if file option is missing while infile is not.

pcm_file: fix SEGFAULT if file option is missing while infile is not.

Commit 5c5f1358123af69155267463a0b6254ad9cbecc4 requires both file and
infile options to be missing to report a failure.
In fact, only file option is mandatory and should be checked there.
Otherwise, NULL file triggers segfault in
snd_pcm_file_replace_fname() called from
snd_pcm_file_open_output_file().
infile option is optional, so don't report fatal error if it's missing.

Signed-off-by: Andrey Mazo <mazo@telum.ru>
Signed-off-by: Takashi Iwai <tiwai@suse.de>