[webconfig] cleanly handles ``fckeditor_installed`` when no uiprops
The previous version of the code relied on a default value with a dummy
``FCKEDITOR_PATH`` entry. The new code check if uiprops is initialized or not.
<div id="ajaxroot">
<div class="ajaxHtmlHead">
<script src="http://foo.js" type="text/javascript"> </script>
<link rel="stylesheet" type="text/css" media="all" href="qunit.css" />
</div>
<h1>Hello</h1>
</div>