Calling set on VariantArray with an out of bounds index causes segfault

[jacobsky]

As mentioned in discord

let vertices : Vec<Vector3> = vec![];
let arrays = VariantArray::new();
arrays.set(ArrayMesh::ARRAY_VERTEX as i32, vertices);

The issue is that VariantArray::set is not an unsafe function.

This should be corrected either by making the function unsafe, or doing some internal bounds checking to be inline with the Rust guidelines.

As a follow-up we should review the VariantArray/Dictionary APIs to ensure there's no other unexpected UB