When deserializing from data, ctor of ACM fails

The collision_mesh param is empty, but its root_name has been set already, so, instead we don't try to do reassign it, it will be deserialized from data.

Author: gonzalocasas

src/compas_fab/robots/planning_scene.py

@@ -170,7 +170,8 @@ class AttachedCollisionMesh(object):
 
     def __init__(self, collision_mesh, link_name, touch_links=None, weight=1.):
         self.collision_mesh = collision_mesh
-        self.collision_mesh.root_name = link_name
+        if self.collision_mesh:
+            self.collision_mesh.root_name = link_name
         self.link_name = link_name
         self.touch_links = touch_links if touch_links else [link_name]
         self.weight = weight