Crash happens in `action_group_colors_set_from_posebone` /
`ANIM_bonecolor_posebone_get` on a `bPoseChannel` without a `bone`.
If I am not mistaken a new `bPoseChannel` (e.g. after duplication) will
only get its `bone` after leaving editmode.
So in a way the situation is similar to 2a8ce1f121
Behavior of `animchan_sync_group` is not reliable in a way that getting
a `bPoseChannel` from an `bActionGroup` will guarantee these are really
corresponding. So usually, if you dulplicate/symmetrize a bone, there
would be no corresponding `bActionGroup` and nothing would happen
really. But you could for example group fcurves from `Bone` under a
group called `Bone.001` and vice versa. This is totally allowed to do.
In this case, `animchan_sync_group` is doing nothing totally helpful, so
it could find the "wrong" `bPoseChannel`. And it could try
`action_group_colors_set_from_posebone` with that `bPoseChannel` which
still does not have a `bone` and then crash.
So now only do this if we have a valid `bone`.
Pull Request: https://projects.blender.org/blender/blender/pulls/118676
a6060ea8ee