Fix handleHelpRequest.

* Make sure we only change our own urls inside that function
* QDesktopService::setUrlHandler expects the target slot to take a QUrl

Reviewed-by: ck

src/plugins/help/helpmanager.cpp

@@ -102,7 +102,7 @@ bool HelpManager::guiEngineNeedsUpdate() const
 
 void HelpManager::handleHelpRequest(const QString &url)
 {
-    emit helpRequested(url);
+    emit helpRequested(QUrl(url));
 }
 
 void HelpManager::verifyDocumenation()