Fix quota error formatting in case of NoneType
[pithos] / htdocs /
drwxr-xr-x   ..
-rw-r--r-- 1272 apple-touch-icon.png
-rw-r--r-- 1150 favicon.ico
lrwxrwxrwx 11 index.html -> pithos.html
-rw-r--r-- 3203 okeanos.html
-rw-r--r-- 5563 pithos.html
drwxr-xr-x - site_media