gtk3: it was pointed out to me we have up and down reversed

by jrb, oops

Change-Id: Id722533edae72d4849129e339bd6cca265d3c35c
Reviewed-on: https://gerrit.libreoffice.org/17578Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>

vcl/unx/gtk3/gdi/gtk3salnativewidgets-gtk.cxx

@@ -134,11 +134,11 @@ Rectangle GtkSalGraphics::NWGetSpinButtonRect( ControlPart nPart, Rectangle aAre
     buttonRect.Bottom() = buttonRect.Top() + aAreaRect.GetHeight();
     if ( nPart == PART_BUTTON_UP )
     {
-        buttonRect.setX(aAreaRect.Left() + (aAreaRect.GetWidth() - 2*buttonRect.GetWidth()));
+        buttonRect.setX(aAreaRect.Left() + (aAreaRect.GetWidth() - buttonRect.GetWidth()));
     }
     else if( nPart == PART_BUTTON_DOWN )
     {
-        buttonRect.setX(aAreaRect.Left() + (aAreaRect.GetWidth() - buttonRect.GetWidth()));
+        buttonRect.setX(aAreaRect.Left() + (aAreaRect.GetWidth() - 2*buttonRect.GetWidth()));
     }
     else
     {