avformat/audiointerleave: Check before dereferencing

In order to use ff_audio_rechunk_interleave() (a special interleavement
function for situations where the ordinary "interleave by dts" is not
appropriate), the AVStreams must have private data and this private data
must begin with an AudioInterleaveContext which contains a fifo that may
need to be freed and when ff_audio_interleave_close() was called, it just
assumed that everything has been properly set up, i.e. that every streams
priv_data exists. This implies that this function can not be called from
the deinit function of a muxer, because such functions might be called
if the private data has not been successfully allocated. In order to
change this, add a check for whether the private data exists before
trying to free the fifo in it.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/audiointerleave.c

@@ -33,7 +33,7 @@ void ff_audio_interleave_close(AVFormatContext *s)
         AVStream *st = s->streams[i];
         AudioInterleaveContext *aic = st->priv_data;
 
-        if (st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO)
+        if (aic && st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO)
             av_fifo_freep(&aic->fifo);
     }
 }