avcodec/alsdec: Check that input space for header exists in read_diff_float_data()

Fixes: Timeout (21sec -> 8sec)
Fixes: 17832/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALS_fuzzer-5737092172218368

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

libavcodec/alsdec.c

@@ -1475,6 +1475,9 @@ static int read_diff_float_data(ALSDecContext *ctx, unsigned int ra_frame) {
         ff_mlz_flush_dict(ctx->mlz);
     }
 
+    if (avctx->channels * 8 > get_bits_left(gb))
+        return AVERROR_INVALIDDATA;
+
     for (c = 0; c < avctx->channels; ++c) {
         if (use_acf) {
             //acf_flag