Ensure arrays are valid when reading instead of evaluation.
In general correcting data in evaluation is error prone since
data may be accessed from other parts of Blender before evaluation
(Python scripts for example), and isn't thread-safe in edit-mode
where the edit-data is shared, see #144970.
This also removes material index correction, this doesn't cause
problems as the evaluated `Nurb` must already support out of range
material indices.
e17677ce73