[Lazarus] Qt Ws doesn't support properly GetWindowSize() and GetWindowRect()

[Giuliano Colla]

This snippet of code, which executes as expected with GTK2 WS, fails 
with QT WS:

> procedure TForm1.btnWsizeClick(Sender: TObject);
> var  aHandle: THandle;
>    aWidth,aHeight: Integer;
>    aRect: TRect;
> begin
>    aHandle:= Form1.Handle;
>    if GetWindowSize(aHandle,aWidth,aHeight) then begin
>      Label3.Caption:= Format('Width: %d Height: %d',[aWidth,aHeight]);
>    end
>    else Label3.Caption:= 'Failed to get Window Size';
>    GetWindowRect(aHandle,aRect);
>    Label3.Caption:= Label3.Caption + Format(' Rect: %d,%d',[
>    aRect.Right-aRect.Left,
>    aRect.Bottom-aRect.Top]);
>    Label3.Visible:= True;
> end;

As it is, it crashes with an AV in the GetWindowSize call. The failing 
call is in TQtWidget.GetWidget: it executes Result := 
QWidgetH(TheObject) where TheObject appears to have taken a bogus value.

If I remove the offending call, then the subsequent GetWindowRect() 
returns bogus values, sort of -32704 and -85984614 instead of 689 and 522.

Under GTK2 both calls work as expected.

Tested under Linux x86_64 (CentOs 6) with Lazarus 1.8 - QT45 - fpc 3.0.4

It doesn't appear to be a regression, because it does the same even with 
a very old Lazarus 1.2.6 , qt45 and fpc 2.6.4

Should I report a bug or is it a known issue?

Giuliano