[WebServer] Loading image failed with libmicrohttpd 0.9.35 #4821

A bug was fixed inside libmicrohttpd : https://gnunet.org/bugs/view.php?id=3371
The path of the url is no longer decoded by libmicrohttpd in version 0.9.35
This bug fix breaks a lot of HTTP request, like loading images...
Fix it by decoding the path inside XBMC.