Avoid overflow in Box<T>::size() for an empty box.
Avoid overflow in Box<T>::size() for an empty box.

oglops/PyIlmBase,oglops/PyIlmBase,oglops/PyIlmBase,oglops/IlmBase,oglops/OpenEXR,oglops/OpenEXR,oglops/IlmBase,oglops/IlmBase,oglops/OpenEXR,oglops/PyIlmBase