Port is now availabel when open and readBytesOnListen bug

[yong5354]

The following are the two problems I met when using:

1. Open port number that is greater than COM9, the open function will return INVALID_HANDLE_VALUE and the error is "COMXX is not available". see this https://support.microsoft.com/en-us/topic/howto-specify-serial-ports-larger-than-com9-db9078a5-b7b6-bf00-240f-f749ebfd913e. so i change the _portNameUtf16 value from TEXT(portName) to TEXT("\\\\.\\$portName") and solve this problem.
2. The value in readBytesOnListen callback will change randomly. This problem is cause because the value in readBytesOnListen callback is cast from a pointer "lpBuffer" that has been free, here is the code i modify:

   -uint8list = lpBuffer.cast<Uint8>().asTypedList(_bytesRead.value);
   +var u8l = lpBuffer.cast<Uint8>().asTypedList(_bytesRead.value); 
   +uint8list = Uint8List.fromList(u8l); //return the copy instead of the direct cast
   free(lpBuffer);

   I'm not sure if this is the correct solution, please point it out if I'm wrong, thanks again for sharing

[FengChendian]

1. Yeah, I didn't implement method to open port number greater than COM9. I will add it later.

2. I think you are right. I was always confused about random wrong [255,...255] data.It seems like that the problem was solved by your method.

   /// [_read] is a fundamental read function/
   Future<Uint8List> _read(int bytesSize) async {
   final lpBuffer = calloc<Uint16>(bytesSize);
   Uint8List uint8list;
   
   try {
     readOnBeforeFunction();
     ReadFile(handler!, lpBuffer, bytesSize, _bytesRead, _over);
   } finally {
     /// Uint16 need to be casted for real Uint8 data
     var u8l = lpBuffer.cast<Uint8>().asTypedList(_bytesRead.value);
     uint8list = Uint8List.fromList(u8l);
     free(lpBuffer);
   }
   
   return uint8list;
   }