Fix NRE on Avalonia for error applets with unknown error message (#3888)

Ryujinx.Ava/Ui/Applet/AvaHostUiHandler.cs

@@ -57,14 +57,14 @@ namespace Ryujinx.Ava.Ui.Applet
 
                     bool opened = false;
 
-                    UserResult response = await ContentDialogHelper.ShowDeferredContentDialog(_parent, 
-                       title, 
-                       message, 
-                       "", 
-                       LocaleManager.Instance["DialogOpenSettingsWindowLabel"], 
-                       "", 
-                       LocaleManager.Instance["SettingsButtonClose"], 
-                       (int)Symbol.Important, 
+                    UserResult response = await ContentDialogHelper.ShowDeferredContentDialog(_parent,
+                       title,
+                       message,
+                       "",
+                       LocaleManager.Instance["DialogOpenSettingsWindowLabel"],
+                       "",
+                       LocaleManager.Instance["SettingsButtonClose"],
+                       (int)Symbol.Important,
                        deferEvent,
                        async (window) =>
                        {
@@ -168,7 +168,7 @@ namespace Ryujinx.Ava.Ui.Applet
 
                     object response = await msgDialog.Run();
 
-                    if (response != null && buttons.Length > 1 && (int)response != buttons.Length - 1)
+                    if (response != null && buttons != null && buttons.Length > 1 && (int)response != buttons.Length - 1)
                     {
                         showDetails = true;
                     }