alsdec: limit avctx->bits_per_raw_sample to 32

avctx->bits_per_raw_sample is used in get_sbits_long, which only
supports up to 32 bits.

CC: libav-stable@libav.org
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>
(cherry picked from commit e191aaca44)
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/alsdec.c

@@ -1641,6 +1641,12 @@ static av_cold int decode_init(AVCodecContext *avctx)
         avctx->sample_fmt          = sconf->resolution > 1
                                      ? AV_SAMPLE_FMT_S32 : AV_SAMPLE_FMT_S16;
         avctx->bits_per_raw_sample = (sconf->resolution + 1) * 8;
+        if (avctx->bits_per_raw_sample > 32) {
+            av_log(avctx, AV_LOG_ERROR, "Bits per raw sample %d larger than 32.\n",
+                   avctx->bits_per_raw_sample);
+            ret = AVERROR_INVALIDDATA;
+            goto fail;
+        }
     }
 
     // set maximum Rice parameter for progressive decoding based on resolution