Different Center of Mass at Load and Runtime Addition

[DavidMansolino]

Describe the Bug
Some robots don't have the same center of mass (CoM) if they are already in the world or added after load.

Steps to Reproduce

1. Open the following world in pause mode: randTerrainStuff1.wbt.zip
2. Copy paste the robot.
3. Check the CoM of both robots in the node editor (with 'including descendants').
4. They are completely different.

Expected behavior
Both centers of masses should strictly be equivalent.

Additional context
The same problem arises when adding from the add node dialog or from a Supervisor.
The problem is also visible with the 'Show Center of Mass' optional rendering.

[DavidMansolino]

There are a few issues with missing bounding objects and density and mass specified together but removing these issues doesn't solve the problem.