Fix clips/masks grouping mode preference reset

This MR fixes #3780 (closed).

The /options/maskobject/grouping preference is of Int type and can be greater than 1, more specifically, it can be 0, 1 or 2. If it was set to 2 ("Put all clipped/masked objects into one group") then on any ungrouping operation the preference will be set to 1 ("Put every clipped/masked object in its own group"). This happens because in the end of sp_item_group_ungroup() function the preference is set with the setBool() method instead of setInt().