Bug 1402292 - Ignore form submission attempt to navigate from already navigated document. r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D163723

docshell/base/nsDocShell.cpp

@@ -13080,8 +13080,7 @@ nsresult nsDocShell::OnLinkClickSync(nsIContent* aContent,
   // window for mScriptGlobal.  If it's not, then we don't want to
   // follow this link.
   nsPIDOMWindowInner* referrerInner = referrerDoc->GetInnerWindow();
-  NS_ENSURE_TRUE(referrerInner, NS_ERROR_UNEXPECTED);
-  if (!mScriptGlobal ||
+  if (!mScriptGlobal || !referrerInner ||
       mScriptGlobal->GetCurrentInnerWindow() != referrerInner) {
     // We're no longer the current inner window
     return NS_OK;