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/PowerLauncher/Helper/ErrorReporting.cs

@@ -3,7 +3,6 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
-using System.Diagnostics;
 using System.Windows;
 using System.Windows.Threading;
 
@@ -67,79 +66,12 @@ namespace PowerLauncher.Helper
                 var logger = LogManager.GetLogger(LoggerName);
                 logger.Error($"From {(isNotUIThread ? "non" : string.Empty)} UI thread's exception: {ExceptionFormatter.FormatException(e)}");
             }
-            else if (IsExceptionFromUserPlugin(e))
-            {
-                // Exceptions thrown by user-installed third-party plugins should be logged
-                // but must not show the crash report window, since the exception is not
-                // caused by PowerToys itself and the popup is confusing and alarming to the user.
-                var logger = LogManager.GetLogger(LoggerName);
-                logger.Error($"From {(isNotUIThread ? "non" : string.Empty)} UI thread - Exception from user plugin: {ExceptionFormatter.FormatException(e)}");
-            }
             else
             {
                 Report(e, isNotUIThread);
             }
         }
 
-        /// <summary>
-        /// Determines whether an exception originated from a user-installed third-party plugin
-        /// (i.e., an assembly loaded from <see cref="Constant.PluginsDirectory"/>).
-        /// </summary>
-        private static bool IsExceptionFromUserPlugin(Exception e)
-        {
-            var current = e;
-            while (current != null)
-            {
-                if (HasPluginStackFrames(current))
-                {
-                    return true;
-                }
-
-                if (current is AggregateException aggregateException)
-                {
-                    foreach (var innerException in aggregateException.InnerExceptions)
-                    {
-                        if (IsExceptionFromUserPlugin(innerException))
-                        {
-                            return true;
-                        }
-                    }
-                }
-
-                current = current.InnerException;
-            }
-
-            return false;
-        }
-
-        private static bool HasPluginStackFrames(Exception e)
-        {
-            try
-            {
-                var pluginsDir = Constant.PluginsDirectory;
-                var stackTrace = new StackTrace(e, fNeedFileInfo: false);
-
-                foreach (var frame in stackTrace.GetFrames() ?? [])
-                {
-                    var assemblyLocation = frame.GetMethod()?.DeclaringType?.Assembly?.Location;
-                    if (!string.IsNullOrEmpty(assemblyLocation) &&
-                        assemblyLocation.StartsWith(pluginsDir, StringComparison.OrdinalIgnoreCase))
-                    {
-                        return true;
-                    }
-                }
-            }
-            catch (System.Exception)
-            {
-                // Reflection-based stack inspection can throw a variety of exceptions
-                // (e.g., SecurityException, TypeLoadException, BadImageFormatException).
-                // In every failure case the safe fallback is to treat the exception as
-                // NOT originating from a plugin so that it still surfaces as a crash report.
-            }
-
-            return false;
-        }
-
         private static void Report(Exception e, bool waitForClose)
         {
             if (e != null)

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)