'code' is used to index a table so make it unsigned

this prevents using negative index and possibly crashing with broken files

Originally committed as revision 16714 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/isom.c

@@ -274,7 +274,7 @@ int ff_mov_iso639_to_lang(const char *lang, int mp4)
     return code;
 }
 
-int ff_mov_lang_to_iso639(int code, char *to)
+int ff_mov_lang_to_iso639(unsigned code, char *to)
 {
     int i;
     /* is it the mangled iso code? */

libavformat/isom.h

@@ -33,7 +33,7 @@ extern const AVCodecTag codec_movaudio_tags[];
 extern const AVCodecTag ff_codec_movsubtitle_tags[];
 
 int ff_mov_iso639_to_lang(const char *lang, int mp4);
-int ff_mov_lang_to_iso639(int code, char *to);
+int ff_mov_lang_to_iso639(unsigned code, char *to);
 
 typedef struct {
     int count;

libavformat/mov.c

@@ -494,7 +494,7 @@ static int mov_read_mdhd(MOVContext *c, ByteIOContext *pb, MOVAtom atom)
     AVStream *st = c->fc->streams[c->fc->nb_streams-1];
     MOVStreamContext *sc = st->priv_data;
     int version = get_byte(pb);
-    int lang;
+    unsigned lang;
 
     if (version > 1)
         return -1; /* unsupported */