fix: prevent underflow when session list is empty (#1060)

## What are the changes about?
Fixes an integer underflow in `min_session_index`, which was computed by subtracting 1 from the session list length without checking for zero. Caused a panic (Debug/ReleaseSafe) or wraparound (ReleaseFast) on installs with no available sessions.

## What existing issue(s) does this resolve?
N/A

## 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`

Co-authored-by: Matheus C. <245040149+matheusc457@users.noreply.github.com>
Reviewed-on: https://codeberg.org/fairyglade/ly/pulls/1060
Reviewed-by: AnErrupTion <anerruption+codeberg@disroot.org>

ly-ui/src/components/generic.zig

@@ -140,6 +140,7 @@ pub fn CyclableLabel(comptime ItemType: type, comptime ChangeItemType: type) typ
         fn goLeft(ptr: *anyopaque) !bool {
             var self: *Self = @ptrCast(@alignCast(ptr));
 
+            if (self.list.items.len == 0) return false;
             self.current = if (self.current == 0) self.list.items.len - 1 else self.current - 1;
 
             if (self.change_item_fn) |change_item_fn| {
@@ -156,6 +157,7 @@ pub fn CyclableLabel(comptime ItemType: type, comptime ChangeItemType: type) typ
         fn goRight(ptr: *anyopaque) !bool {
             var self: *Self = @ptrCast(@alignCast(ptr));
 
+            if (self.list.items.len == 0) return false;
             self.current = if (self.current == self.list.items.len - 1) 0 else self.current + 1;
 
             if (self.change_item_fn) |change_item_fn| {

src/main.zig

@@ -1148,7 +1148,7 @@ pub fn main(init: std.process.Init) !void {
     // Skip if autologin is active to prevent overriding autologin session
     var default_input = state.config.default_input;
 
-    const min_session_index = state.session.label.list.items.len - 1;
+    const min_session_index = if (state.session.label.list.items.len == 0) 0 else state.session.label.list.items.len - 1;
 
     if (state.config.save_file_dir != null and !state.is_autologin) {
         if (state.login_text) |box| {