Move theme initialization to the correct place

DiscordChatExporter.Gui/App.axaml.cs

@@ -96,9 +96,6 @@ public class App : Application, IDisposable
 
     public override void OnFrameworkInitializationCompleted()
     {
-        // Initialize the default theme, before a custom one (if any) is applied by loading settings
-        InitializeTheme();
-
         // Load settings
         _settingsService.Load();
 
@@ -117,6 +114,9 @@ public class App : Application, IDisposable
             desktop.Exit += (_, _) => Dispose();
         }
 
+        // Initialize the theme for the first time; must be done after the main window is created
+        InitializeTheme();
+
         base.OnFrameworkInitializationCompleted();
     }