avformat/mux: fix "no tag found" check in validate_codec_tag()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mux.c

@@ -189,7 +189,7 @@ static int validate_codec_tag(AVFormatContext *s, AVStream *st)
     const AVCodecTag *avctag;
     int n;
     enum AVCodecID id = AV_CODEC_ID_NONE;
-    unsigned int tag  = 0;
+    int64_t tag  = -1;
 
     /**
      * Check that tag + id is in the table
@@ -212,7 +212,7 @@ static int validate_codec_tag(AVFormatContext *s, AVStream *st)
     }
     if (id != AV_CODEC_ID_NONE)
         return 0;
-    if (tag && (st->codec->strict_std_compliance >= FF_COMPLIANCE_NORMAL))
+    if (tag >= 0 && (st->codec->strict_std_compliance >= FF_COMPLIANCE_NORMAL))
         return 0;
     return 1;
 }