lavd/pulse_audio_dec: use default source when no input provided

PulseAudio expilitly requires name of the source.
This patch makes it use default source when not provided.
It simplifies programistic use.
Signed-off-by: Lukasz Marek <lukasz.m.luki2@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavdevice/pulse_audio_dec.c

@@ -154,7 +154,7 @@ static av_cold int pulse_read_header(AVFormatContext *s)
 
     attr.fragsize = pd->fragment_size;
 
-    if (strcmp(s->filename, "default"))
+    if (s->filename[0] != '\0' && strcmp(s->filename, "default"))
         device = s->filename;
 
     if (!(pd->mainloop = pa_threaded_mainloop_new())) {