Bounding box is now shown if bbox is null but enableSelectingObjects is true

[jscastro76]

Describe the bug
The bounding box in some objects is not shown if bbox is not defined in the options properties, but enableSelectingObjects: true in threebox constructor only for cloned objects. Even

To Reproduce
Steps to reproduce the behavior:

1. Set enableSelectingObjects: true in threebox constructor
2. Load and add twice the same 3D model
3. Mouse over the first object (original) and the second (clone)

Expected behavior
Bounding box should be shown in both, but it's only shown in the first, because clones of 3D models do not call utils._validate

• Version 2.1.9

[jscastro76]

Related to #168 changes