Add a button widget to the button list of the selected Radio button group. The function makes sure the radio button grp is valid and the button widget to be added is not already a part of the group. The button is then added as the last button in the group button list

LIB_EXPORT leResult leRadioButtonGroup_AddButton(
    leRadioButtonGroup* grp, 
    leRadioButtonWidget* btn
);

leResult