if the same name is set via gimp_object_set_static_name() or
gimp_object_take_name() (gimp_object_set_name() and
gimp_object_set_name_safe() already had the check).

Since this is a slight behavior change it might have subtle side
effects; it definitely fixes GimpThumbBox thumbnail state to not
always re-create the thumbnail on click, which was happening since
porting to GFile (which switched from gimp_object_set_name() to
gimp_object_take_name()).