Bug 1310156 - Add a null check to nsExpatDriver::HandleError to prevent crashes while determining whether to suppress console error messages. r=smaug

parser/htmlparser/nsExpatDriver.cpp

@@ -969,10 +969,12 @@ nsExpatDriver::HandleError()
     }
   }
 
+  if (mOriginalSink) {
     nsCOMPtr<nsIDocument> doc = do_QueryInterface(mOriginalSink->GetTarget());
     if (doc && doc->SuppressParserErrorConsoleMessages()) {
       shouldReportError = false;
     }
+  }
 
   if (shouldReportError) {
     nsCOMPtr<nsIConsoleService> cs