Blender Git Loki

Fix T92083: Crash renaming bone used in Armature modifier on curve

This is caused by {rB3b6ee8cee708}.

Since rigging curves with armatures only works with envelopes (if I am
not mistaken), this stirs up the question again why we actually give the
choice for vertex groups in parenting. Anyways, curves can have armature
modifiers and renaming bones should not crash.

Now make sure we only go down the route of `BKE_object_defgroup_list`
and `BKE_object_defgroup_find_name` if vertex groups are actually
supported.

Maniphest Tasks: T92083

Differential Revision: https://developer.blender.org/D12876