src: fix warnings in aliased_buffer

* Unary minus usages on unsigned type
* Implicit casts to/from input parameters

PR-URL: https://github.com/nodejs/node/pull/19665


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>