Fix T50306: Unexpected behavior with brilliant diamond object.

Just use `object_utils.object_data_add()` as everyone else...

add_mesh_extra_objects/add_mesh_round_brilliant.py

@@ -219,11 +219,11 @@ def addBrilliant(context, s, table_w, crown_h, girdle_t, pavi_d, bezel_f,
     dmesh = bpy.data.meshes.new("dmesh")
     dmesh.from_pydata(Verts, [], Faces)
     dmesh.update()
-    dobj = bpy.data.objects.new("dobj", dmesh)
 
-    # link object into scene
-    scene.objects.link(dobj)
-    
+    # Create object and link it into scene.
+    from bpy_extras import object_utils
+    dobj = object_utils.object_data_add(context, dmesh, operator=None, name="dobj").object
+
     # activate and select object
     scene.objects.active = dobj
     dobj.select = True