movenc: Free the buffer returned by url_close_dyn_buffer, regardless of the size

This fixes a leak introduced in rev 23942, since we write padding to the
buffer unconditionally.

Originally committed as revision 24342 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/movenc.c

@@ -1630,8 +1630,8 @@ static int mov_write_udta_tag(ByteIOContext *pb, MOVMuxContext *mov,
         put_be32(pb, size+8);
         put_tag(pb, "udta");
         put_buffer(pb, buf, size);
-        av_free(buf);
     }
+    av_free(buf);
 
     return 0;
 }