Fixed long-running operations on SnackBarMessage callback (#2627) (#2631)

actionClickWaitHandle will be disposed after message auto-closed. We need to avoid call any methods on disposed EventWaitHandle, need to check is it closed (disposed) or invalid

Co-authored-by: Andrey Nasonov <[email protected]>

Author: Erapchu

MaterialDesignThemes.Wpf/SnackbarMessageQueue.cs

@@ -384,6 +384,11 @@ private static Tuple<SnackbarMessage, MouseNotOverManagedWaitHandle> CreateAndSh
             {
                 if (++clickCount == 1)
                     DoActionCallback(messageQueueItem);
+
+                // Don't operate with eventWaitHandle if disposed/invalid
+                if (actionClickWaitHandle.SafeWaitHandle.IsInvalid || actionClickWaitHandle.SafeWaitHandle.IsClosed)
+                    return;
+
                 actionClickWaitHandle.Set();
             };
             snackbar.SetCurrentValue(Snackbar.MessageProperty, snackbarMessage);