The armature modifier calls `BKE_armature_deform_coords_with_mesh` (and
thus `BKE_id_defgroup_list_get`) for legacy curves as well, these are
only "riggable" via envelope weights though (this situation could be
made a bit clearer when parenting -- which is for another commit
though).
So to avoid the (rightful) assert in `BKE_id_defgroup_list_get`, only
call it in case vertex groups are supported (and possibly used later on
-- which is never the case for legacy curves).
Note: this was reported in chat by @LazyDodo because the CurveArmature
test was failing in debug
Pull Request: https://projects.blender.org/blender/blender/pulls/128792
da9cf98324