WPF/OffScreen - Avoid ObjectDisposedException when browser is already disposed (#4941)

Author: campersau

CefSharp.OffScreen/ChromiumWebBrowser.cs

@@ -291,7 +291,10 @@ protected virtual void Dispose(bool disposing)
                 //Stop rendering immediately so later on when we dispose of the
                 //RenderHandler no further OnPaint calls take place
                 //Check browser not null as it's possible to call Dispose before it's created
-                browser?.GetHost().WasHidden(true);
+                if (browser?.IsDisposed == false)
+                {
+                    browser?.GetHost().WasHidden(true);
+                }
 
                 // Don't reference event listeners any longer:
                 AddressChanged = null;

CefSharp.Wpf/ChromiumWebBrowser.cs

@@ -671,7 +671,10 @@ private void InternalDispose(bool disposing)
                 //Stop rendering immediately so later on when we dispose of the
                 //RenderHandler no further OnPaint calls take place
                 //Check browser not null as it's possible to call Dispose before it's created
-                browser?.GetHost().WasHidden(true);
+                if (browser?.IsDisposed == false)
+                {
+                    browser?.GetHost().WasHidden(true);
+                }
 
                 UiThreadRunAsync(() =>
                 {