au: do not arbitrarily limit channel count

Nothing in the AU specification sets a limit on channel count.
We only need to avoid an overflow in the packet size calculation.

libavformat/au.c

@@ -57,6 +57,8 @@ static int au_probe(AVProbeData *p)
         return 0;
 }
 
+#define BLOCK_SIZE 1024
+
 /* au input */
 static int au_read_header(AVFormatContext *s)
 {
@@ -92,7 +94,7 @@ static int au_read_header(AVFormatContext *s)
         return AVERROR_PATCHWELCOME;
     }
 
-    if (channels == 0 || channels > 64) {
+    if (channels == 0 || channels >= INT_MAX / (BLOCK_SIZE * bps >> 3)) {
         av_log(s, AV_LOG_ERROR, "Invalid number of channels %d\n", channels);
         return AVERROR_INVALIDDATA;
     }
@@ -117,8 +119,6 @@ static int au_read_header(AVFormatContext *s)
     return 0;
 }
 
-#define BLOCK_SIZE 1024
-
 static int au_read_packet(AVFormatContext *s,
                           AVPacket *pkt)
 {