Installation Wizard: Fix endless loop trying to request .../images/brand...

If the IIS "Anonymous Authentication Identity" has no read permission on file system there is an endless loop in the Installation Wizard that tries to load the file /images/branding/DNN_logo.png again and again. In detail, the onerror trigger for the banner image is fired, the handler changes the image source and the onerror trigger is fired again.

Of course the installation is completely broken (as described here http://blog.janjonas.net/2014-07-02/dotnetnuke-fix-broken-installation-wizard) but this endless loop makes it hard to debug because the browser console is flooded and it seems, that the page does not stop loading (tested in Firefox 30).