SaveAs returns its window id as an unsigned value.

[laurenrad]

riscos-toolbox/riscos_toolbox/objects/saveas.py

Line 41 in 9a7c5ef

return self._miscop_get_unsigned(SaveAs.GetWindowId)

The getter for the window_id property here uses _miscop_get_unsigned but as per issues #75 and #78 IDs are signed elsewhere. This should be changed to use _miscop_get_signed instead. See also issue #98.