RNA Bugfix:

RNA Bugfix:

The following script would fail:
#ob = bpy.context.active_object
pb = bpy.context.active_pose_bone
pb.bone.driver_add("hide")  # <--- exception here

The RNA-path function for Bone assumed that when it got called, it's
"id_data" (or owner-idblock-pointer) would only be ID_AR (i.e. an
armature). However, in the above example, pb.bone has ob as its
id_data, resulting in an invalid RNA path getting created. Added check
for this case, since it's likely to be common