avcodec/utils: Check bits_per_coded_sample

This avoids the need for each decoder separately having to handle this case

Fixes: shift exponent -100663046 is negative
Fixes: out of array access
Fixes: 15270/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_IFF_ILBM_fuzzer-5727829913763840

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

libavcodec/utils.c

@@ -962,6 +962,10 @@ FF_ENABLE_DEPRECATION_WARNINGS
             ret = AVERROR(EINVAL);
             goto free_and_end;
         }
+        if (avctx->bits_per_coded_sample < 0) {
+            ret = AVERROR(EINVAL);
+            goto free_and_end;
+        }
         if (avctx->sub_charenc) {
             if (avctx->codec_type != AVMEDIA_TYPE_SUBTITLE) {
                 av_log(avctx, AV_LOG_ERROR, "Character encoding is only "