avformat/segafilm: Check that there is a stream

Fixes: assertion failure
Fixes: 26472/clusterfuzz-testcase-minimized-ffmpeg_dem_SEGAFILM_fuzzer-5759751591559168

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/segafilm.c

@@ -144,6 +144,9 @@ static int film_read_header(AVFormatContext *s)
         film->video_type = AV_CODEC_ID_NONE;
     }
 
+    if (!film->video_type && !film->audio_type)
+        return AVERROR_INVALIDDATA;
+
     /* initialize the decoder streams */
     if (film->video_type) {
         st = avformat_new_stream(s, NULL);