sizing button wrong in ListBox::Resize

Passing a right edge co-ordinate to a width param, ever since
   commit 4849fb6d
   Date:   Mon May 10 14:47:20 2004 +0000
   INTEGRATION: CWS nwf (1.25.36); FILE MERGED

Probably only works because the button is on the right edge, and
consequently the width will be clamped to the widget area.

Change-Id: I28a88cd298bc5beb20162f457c7cc125e1d0303a
Reviewed-on: https://gerrit.libreoffice.org/72231
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

vcl/source/control/listbox.cxx

@@ -590,14 +590,13 @@ void ListBox::Resize()
         if ( GetNativeControlRegion( ControlType::Listbox, ControlPart::ButtonDown,
                     aArea, ControlState::NONE, aControlValue, aBound, aContent) )
         {
-            long nTop = 0;
             // Convert back from border space to local coordinates
             aPoint = pBorder->ScreenToOutputPixel( OutputToScreenPixel( aPoint ) );
             aContent.Move( -aPoint.X(), -aPoint.Y() );
 
             // Use the themes drop down size for the button
             aOutSz.setWidth( aContent.Left() );
-            mpBtn->setPosSizePixel( aContent.Left(), nTop, aContent.Right(), (nBottom-nTop) );
+            mpBtn->setPosSizePixel( aContent.Left(), 0, aContent.GetWidth(), nBottom );
 
             // Adjust the size of the edit field
             if ( GetNativeControlRegion( ControlType::Listbox, ControlPart::SubEdit,