Coil is visible when opening a new project or starting a new session without recovering the previous state

[henrikkauppi]

When opening a new project or starting a new session without loading the previous state, the coil is immediately visible in the volume viewer.

The issue can be reproduced by:

1. Creating a new coil registration
2. Closing InVesalius without saving the state
3. Opening a new project or InVesalius session