Presumably also the author has now learned this, after discovering at the end that compiling with the sanitizer enabled immediately showed which is the bug, which would have saved a lot of time if he had always used it.

Unfortunately Doom has a lot of undefined behavior (because it's a 30 year old codebase) so if you enable UBSAN you're inundated with warnings. Finding this specific needle in that haystack would take quite a lot of effort.