Set the type of size in COOKSubpacket to unsigned

Originally committed as revision 18691 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/cook.c

@@ -72,7 +72,7 @@ typedef struct {
 
 typedef struct {
     int                 ch_idx;
-    int                 size;
+    unsigned int        size;
     int                 num_channels;
     int                 cookversion;
     int                 samples_per_frame;