Fix user detection if /etc/login.defs does not contain both UID_MIN and UID_MAX (#1014)

## What are the changes about?

I modified getUserIdRange(), so it checks if either of UID_MIN and UID_MAX is set in /etc/login.defs. If any, but not both, is not set, it uses fallback value. I don't know zig build system, so I added ugly fallback values passthrough.

## What existing issue does this resolve?

#1013

## Pre-requisites

- [X] I have tested & confirmed the changes work locally
- [X] I have read and fully adhere to the rules set in the contributing guidelines found in `CONTRIBUTING.md`

Reviewed-on: https://codeberg.org/fairyglade/ly/pulls/1014
Reviewed-by: AnErrupTion <anerruption+codeberg@disroot.org>

build.zig

@@ -75,6 +75,8 @@ pub fn build(b: *std.Build) !void {
         .target = target,
         .optimize = optimize,
         .enable_x11_support = enable_x11_support,
+        .fallback_uid_min = fallback_uid_min,
+        .fallback_uid_max = fallback_uid_max
     });
     exe.root_module.addImport("ly-ui", ly_ui.module("ly-ui"));