RangeCheck error in ConvertUTF8ToUTF16

• Lazarus/FPC Version: 2.3

The below will raise a range check error.

at line 3676

              // to double wide char UTF-16 char
              C:=C-$10000;

C will be 40197. C is Cardinal. Subtracting 65536 fails.

As a side note:

Name: ConvertUTF8ToUTF16 Params: SrcCharCount - Char count allocated in source string

It appears SrcCharCount is really the byte-length. For a function that (by name) takes Utf8 as Source this should be made clear.
Yes, Src is a PChar, meaning the pascal type of 8bit-char. But its ambiguous.

program Project1;
{$mode objfpc}{$H+}
uses
  LazUTF8
  { you can add units after this };

const
  a: array[0..4] of char = (
    #240, #139, #128, #172, #0
  );

var
  b: array[0..9] of WideChar;
  l: SizeUInt;

begin
  ConvertUTF8ToUTF16(@b, 9, @a,4, [toInvalidCharToSymbol], l);
end.