avcodec/libfdk-aacdec: Correct buffer_size parameter

the timeDataSize argument to aacDecoder_DecodeFrame() seems undocumented and until
2016 04 (203e3f28fb) unused.
after that commit libfdk-aacdec interprets it as size in sample units and memsets that on error.
FFmpeg as well as others (like GStreamer) did interpret it as size in bytes

Fixes: 1442/clusterfuzz-testcase-minimized-4540199973421056 (This requires recent libfdk to reproduce)

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

libavcodec/libfdk-aacdec.c

@@ -325,7 +325,7 @@ static int fdk_aac_decode_frame(AVCodecContext *avctx, void *data,
         return AVERROR_INVALIDDATA;
     }
 
-    err = aacDecoder_DecodeFrame(s->handle, (INT_PCM *) s->decoder_buffer, s->decoder_buffer_size, 0);
+    err = aacDecoder_DecodeFrame(s->handle, (INT_PCM *) s->decoder_buffer, s->decoder_buffer_size / sizeof(INT_PCM), 0);
     if (err == AAC_DEC_NOT_ENOUGH_BITS) {
         ret = avpkt->size - valid;
         goto end;