Paging Implemenation: Don't map page at address zero

[phil-opp]

The Rust standard library does not allow writes to address 0, so this can lead to problems. In the post, we don't write to address 0 directly, so this isn't an immediate problem, but it's nonetheless dangerous.

Reported in #570 (comment).

[pitust]

Idea: We shouldn't map pages to virtual address zero

[phil-opp]

I think mapping pages to the physical frame at address zero is fine. But we should not map the page at virtual address zero.

[pitust]

yes, that is what i meant.