[Crash] Fixed occasional crash when extracting form data from page.

Apparently, QWebFrame::childFrames can return NULL frame.

src/lib/autofill/pageformcompleter.cpp

@@ -239,8 +239,10 @@ QWebElementCollection PageFormCompleter::getAllElementsFromPage(QWebPage* page,
     frames.append(page->mainFrame());
     while (!frames.isEmpty()) {
         QWebFrame* frame = frames.takeFirst();
-        list.append(frame->findAllElements(selector));
-        frames += frame->childFrames();
+        if (frame) {
+            list.append(frame->findAllElements(selector));
+            frames += frame->childFrames();
+        }
     }
 
     return list;