avformat/rka: Fix 1/0 with bps=1

Fixes: division by zero
Fixes: 55940/clusterfuzz-testcase-minimized-ffmpeg_IO_DEMUXER_fuzzer-6333107679920128

The decoder does not support bps=1 and i have no such sample so it is not
known if this duration is correct. Alternatively we could error out on all
bps we currently do not support on the decoder side or not set duration.

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

libavformat/rka.c

@@ -114,7 +114,7 @@ static int rka_read_header(AVFormatContext *s)
     par->ch_layout.nb_channels = channels;
     par->sample_rate = samplerate;
     par->bits_per_raw_sample = bps;
-    st->duration = nb_samples / (channels * (bps >> 3));
+    st->duration = 8LL*nb_samples / (channels * bps);
 
     if (s->pb->seekable & AVIO_SEEKABLE_NORMAL)
         ff_ape_parse_tag(s);