WPF - Improve ChromiumWebBrowser Dispose

- RenderHandler wasn't being disposed at all
- Used newer syntax for null Dispose calls

Author: amaitland

CefSharp.Wpf/ChromiumWebBrowser.cs

@@ -673,11 +673,8 @@ private void InternalDispose(bool disposing)
                 browser = null;
 
                 // Incase we accidentally have a reference to the CEF drag data
-                if (currentDragData != null)
-                {
-                    currentDragData.Dispose();
-                    currentDragData = null;
-                }
+                currentDragData?.Dispose();
+                currentDragData = null;
 
                 PresentationSource.RemoveSourceChangedHandler(this, PresentationSourceChangedHandler);
                 // Release window event listeners if PresentationSourceChangedHandler event wasn't
@@ -715,17 +712,18 @@ private void InternalDispose(bool disposing)
                     CleanupElement.Unloaded -= OnCleanupElementUnloaded;
                 }
 
-                if (managedCefBrowserAdapter != null)
-                {
-                    managedCefBrowserAdapter.Dispose();
-                    managedCefBrowserAdapter = null;
-                }
+                managedCefBrowserAdapter?.Dispose();
+                managedCefBrowserAdapter = null;
 
                 // LifeSpanHandler is set to null after managedCefBrowserAdapter.Dispose so ILifeSpanHandler.DoClose
                 // is called.
                 LifeSpanHandler = null;
 
-                WpfKeyboardHandler.Dispose();
+                WpfKeyboardHandler?.Dispose();
+                WpfKeyboardHandler = null;
+
+                RenderHandler?.Dispose();
+                RenderHandler = null;
 
                 source = null;
             }