Allocating full size >512 returns None

[Swoorup]

Creating and then allocating the same size for anything over 512 results in allocation failure.

#[test]
fn test_allocator() {
    let requested = 513;
    let mut allocator: Allocator<u32> = Allocator::new(requested);
    let result = allocator.allocate(requested);
    assert!(result.is_some());
}