Extra non-pumping lock point

src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs

@@ -366,6 +366,7 @@ namespace Avalonia.Win32
 
                 case WindowsMessage.WM_SIZE:
                     {
+                        using(NonPumpingSyncContext.Use())
                         using (_rendererLock.Lock())
                         {
                             // Do nothing here, just block until the pending frame render is completed on the render thread