fix(Settings): handle null Exception in Frame_NavigationFailed to prevent NullReferenceException

When NavigationFailedEventArgs.Exception is null, the original code threw a
NullReferenceException instead of a meaningful error. Use null-coalescing to
throw an InvalidOperationException with context about the failed page.

src/modules/launcher/Plugins/Microsoft.Plugin.Program/Programs/UWPApplication.cs

@@ -207,7 +207,6 @@ namespace Microsoft.Plugin.Program.Programs
         {
             var appManager = new ApplicationActivationHelper.ApplicationActivationManager();
             const ApplicationActivationHelper.ActivateOptions noFlags = ApplicationActivationHelper.ActivateOptions.None;
-            var type = GetType();
             await Task.Run(() =>
             {
                 try
@@ -216,7 +215,7 @@ namespace Microsoft.Plugin.Program.Programs
                 }
                 catch (Exception ex)
                 {
-                    ProgramLogger.Exception($"Unable to launch UWP {DisplayName}", ex, type, queryArguments);
+                    ProgramLogger.Exception($"Unable to launch UWP {DisplayName}", ex, MethodBase.GetCurrentMethod().DeclaringType, queryArguments);
                     var name = "Plugin: " + Properties.Resources.wox_plugin_program_plugin_name;
                     var message = $"{Properties.Resources.powertoys_run_plugin_program_uwp_failed}: {DisplayName}";
                     api.ShowMsg(name, message, string.Empty);

src/settings-ui/Settings.UI/ViewModels/ShellViewModel.cs

@@ -135,7 +135,8 @@ namespace Microsoft.PowerToys.Settings.UI.ViewModels
 
         private void Frame_NavigationFailed(object sender, NavigationFailedEventArgs e)
         {
-            throw e.Exception;
+            throw e.Exception ?? new InvalidOperationException(
+                $"Navigation to {e.SourcePageType?.FullName ?? "unknown page"} failed.");
         }
 
         private void Frame_Navigated(object sender, NavigationEventArgs e)