Bug 752426 - Add null checks for thumbnail screenshots. r=blassey

widget/android/AndroidBridge.cpp

@@ -2402,10 +2402,14 @@ nsresult AndroidBridge::TakeScreenshot(nsIDOMWindow *window, PRInt32 srcX, PRInt
         nsCOMPtr<nsIDOMDocument> doc;
         rv = window->GetDocument(getter_AddRefs(doc));
         NS_ENSURE_SUCCESS(rv, rv);
+        if (!doc)
+            return NS_ERROR_FAILURE;
 
         nsCOMPtr<nsIDOMElement> docElement;
         rv = doc->GetDocumentElement(getter_AddRefs(docElement));
         NS_ENSURE_SUCCESS(rv, rv);
+        if (!docElement)
+            return NS_ERROR_FAILURE;
 
         PRInt32 viewportHeight;
         PRInt32 pageWidth;