xwma: Avoid division by zero

Reported-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org
Signed-off-by: Martin Storsjö <martin@martin.st>
(cherry picked from commit adc09136a4)
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

libavformat/xwma.c

@@ -200,6 +200,14 @@ static int xwma_read_header(AVFormatContext *s)
 
         /* Estimate the duration from the total number of output bytes. */
         const uint64_t total_decoded_bytes = dpds_table[dpds_table_size - 1];
+
+        if (!bytes_per_sample) {
+            av_log(s, AV_LOG_ERROR,
+                   "Invalid bits_per_coded_sample %d for %d channels\n",
+                   st->codec->bits_per_coded_sample, st->codec->channels);
+            return AVERROR_INVALIDDATA;
+        }
+
         st->duration = total_decoded_bytes / bytes_per_sample;
 
         /* Use the dpds data to build a seek table.  We can only do this after