avcodec/osq: Treat sum = 0 as k = 0

We have no valid sample that triggers this so we do not know if this would decode
correctly, but -inf is not the correct k value

Fixes: Assertion n>=0 && n<=32 failed at libavcodec/get_bits.h:423
Fixes: -inf is outside the range of representable values of type 'int'
Fixes: 70709/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_OSQ_fuzzer-6223623839350784

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg

libavcodec/osq.c

@@ -160,6 +160,8 @@ static int update_residue_parameter(OSQChannel *cb)
     int rice_k;
 
     sum = cb->sum;
+    if (!sum)
+        return 0;
     x = sum / cb->count;
     rice_k = ceil(log2(x));
     if (rice_k >= 30) {