rawdec: use a default sample rate if none is specified.

Fixes "ffmpeg -f s16le -i /dev/zero"
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/rawdec.c

@@ -57,9 +57,9 @@ int ff_raw_read_header(AVFormatContext *s, AVFormatParameters *ap)
             if (s1 && s1->sample_rate)
                 st->codec->sample_rate = s1->sample_rate;
             if (st->codec->sample_rate <= 0) {
-                av_log(s, AV_LOG_ERROR, "Invalid sample rate %d specified\n",
+                av_log(s, AV_LOG_WARNING, "Invalid sample rate %d specified using default of 44100\n",
                        st->codec->sample_rate);
-                return AVERROR(EINVAL);
+                st->codec->sample_rate= 44100;
             }
 
             if (s1 && s1->channels)