avcodec/scpr: check remaining data after decode

Fixes Timeout (29sec -> 14sec)
Fixes: 13713/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SCPR_fuzzer-5756778069884928

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

libavcodec/scpr.c

@@ -575,6 +575,9 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
     if (ret < 0)
         return ret;
 
+    if (bytestream2_get_bytes_left(gb) > 5)
+        return AVERROR_INVALIDDATA;
+
     if (avctx->bits_per_coded_sample != 16) {
         ret = av_frame_ref(data, s->current_frame);
         if (ret < 0)