crash after deleting ship designs

[Goncyn]

Reproduction steps:

1. Enter the battle deployment screen.
2. Click the ship design button.
3. Click “Load”
4. Delete a ship design.
5. Click “Go back”
6. Click the ship design button.

The game crashes with the message “Ship Hull not found ->order_salvation_fighter:…\src\SIM_ShipHull.cpp 482” in the log.