Extract app shutdown fallback into App.Shutdown (#1539)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

DiscordChatExporter.Gui/App.axaml.cs

@@ -7,6 +7,7 @@ using Avalonia.Platform;
 using DiscordChatExporter.Gui.Framework;
 using DiscordChatExporter.Gui.Localization;
 using DiscordChatExporter.Gui.Services;
+using DiscordChatExporter.Gui.Utils.Extensions;
 using DiscordChatExporter.Gui.ViewModels;
 using DiscordChatExporter.Gui.ViewModels.Components;
 using DiscordChatExporter.Gui.ViewModels.Dialogs;
@@ -17,7 +18,7 @@ using PowerKit.Extensions;
 
 namespace DiscordChatExporter.Gui;
 
-public class App : Application, IDisposable
+public partial class App : Application, IDisposable
 {
     private readonly ServiceProvider _services;
     private readonly SettingsService _settingsService;
@@ -135,3 +136,12 @@ public class App : Application, IDisposable
         _services.Dispose();
     }
 }
+
+public partial class App
+{
+    public static void Shutdown(int exitCode = 0)
+    {
+        if (Current?.ApplicationLifetime?.TryShutdown(exitCode) != true)
+            Environment.Exit(exitCode);
+    }
+}

DiscordChatExporter.Gui/ViewModels/MainViewModel.cs

@@ -1,7 +1,5 @@
-using System;
 using System.Diagnostics;
 using System.Threading.Tasks;
-using Avalonia;
 using DiscordChatExporter.Gui.Framework;
 using DiscordChatExporter.Gui.Localization;
 using DiscordChatExporter.Gui.Services;
@@ -88,8 +86,7 @@ public partial class MainViewModel(
                 {
                     updateService.FinalizeUpdate(true);
 
-                    if (Application.Current?.ApplicationLifetime?.TryShutdown(2) != true)
-                        Environment.Exit(2);
+                    App.Shutdown(2);
                 }
             );
         }