[Spreadsheet] fix bug where duplicate / bad aliases were being allowed.
[Spreadsheet] fix bug where duplicate / bad aliases were being allowed.

Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master