Additional checks/calls for cases when WebUI may be already gone but OOBE screen instance is not

chrome/browser/ui/webui/chromeos/login/network_screen_handler.cc

Index: chrome/browser/ui/webui/chromeos/login/network_screen_handler.cc
diff --git a/chrome/browser/ui/webui/chromeos/login/network_screen_handler.cc b/chrome/browser/ui/webui/chromeos/login/network_screen_handler.cc
index 89b6da43b940f489d197a69a996ac73943462d9f..158fdf8290226cdf6ed1ce89696b21537670a77b 100644
--- a/chrome/browser/ui/webui/chromeos/login/network_screen_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/network_screen_handler.cc
@@ -47,6 +47,8 @@ NetworkScreenHandler::NetworkScreenHandler()
 }
 
 NetworkScreenHandler::~NetworkScreenHandler() {
+  if (screen_)
+    screen_->OnActorDestroyed(this);
 }
 
 // NetworkScreenHandler, NetworkScreenActor implementation: --------------------
@@ -151,7 +153,8 @@ void NetworkScreenHandler::RegisterMessages() {
 
 void NetworkScreenHandler::HandleOnExit(const ListValue* args) {
   ClearErrors();
-  screen_->OnContinuePressed();
+  if (screen_)
+    screen_->OnContinuePressed();
 }
 
 void NetworkScreenHandler::HandleOnLanguageChanged(const ListValue* args) {