Compare copyright prefix in a more encoding safe way

id is a ASCII-8BIT string but the literal "\xa9" could be
UTF-8 string which in that case Ruby won't conceder them equal.
This is probably because "\xa9" is an invalid UTF-8 string etc.

"\xa9".force_encoding(Encoding::ASCII_8BIT) == "\xa9".force_encoding(Encoding::UTF_8) => false

lib/mp4info.rb

@@ -155,7 +155,7 @@ def parse_atom(io_stream, level, parent_size)
         raise "Parse error"
       end
 
-      if id.unpack("M")[0][0] == "\xA9"
+      if id[0].ord == 0xa9
         # strip copyright sign at the beginning
         id = id[1..-1]
       end