gtk.RadioButton and RadioMenuItem: Allow usage of nil group pointers. When creating a radio button, or setting its group, we should be able to use a nil reference. This allow creating the first button when we still don't have the group, or unsetting the group of a button.
gtk.RadioButton and RadioMenuItem: Allow usage of nil group pointers.
When creating a radio button, or setting its group, we should be able to use a nil reference.
This allow creating the first button when we still don't have the group, or unsetting the group of a button.

pekim/gotk3,gotk3/gotk3,pekim/gotk3,gotk3/gotk3,pekim/gotk3