avcodec/alac: Check for bps of 0

Fixes: shift exponent 32 is too large for 32-bit type 'unsigned int'
Fixes: 15764/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALAC_fuzzer-5102101203517440

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

libavcodec/alac.c

@@ -250,10 +250,12 @@ static int decode_element(AVCodecContext *avctx, AVFrame *frame, int ch_index,
 
     alac->extra_bits = get_bits(&alac->gb, 2) << 3;
     bps = alac->sample_size - alac->extra_bits + channels - 1;
-    if (bps > 32U) {
+    if (bps > 32) {
         avpriv_report_missing_feature(avctx, "bps %d", bps);
         return AVERROR_PATCHWELCOME;
     }
+    if (bps < 1)
+        return AVERROR_INVALIDDATA;
 
     /* whether the frame is compressed */
     is_compressed = !get_bits1(&alac->gb);