TBufferedFileStream cannot execute SetSize(0) on newly created file
```
program Project1;
{$mode objfpc}{$H+}
uses
{$IFDEF UNIX}
cthreads,
{$ENDIF}
SysUtils,
Classes,
bufstream;
var
LStream: TBufferedFileStream;
begin
LStream := TBufferedFileStream.Create('test.txt', fmCreate or fmShareDenyWrite);
try
LStream.Size := 0; // This will cause a system exception.
Readln;
finally
FreeAndNil(LStream);
end;
end.
```
issue