Fix ReferenceError in update_bbox_accumulation

Guard against objects that have already been removed from
Blender's data (StructRNA removed) before the function runs.
This occurs when switch_representation is called on temporary
annotation objects that are freed before returning.

Generated with the assistance of an AI coding tool.

src/bonsai/bonsai/tool/geometry.py

@@ -2477,7 +2477,10 @@ class Geometry(bonsai.core.tool.Geometry):
         Stores the union of all representation bboxes ever loaded for this object as
         ``obj["ifc_bbox_min"]`` and ``obj["ifc_bbox_max"]`` in object-local space.
         """
-        if not obj.bound_box:
+        try:
+            if not obj.bound_box:
+                return
+        except ReferenceError:
             return
         corners = obj.bound_box
         xs = [v[0] for v in corners]