XWIKI-8265: Can't delete dangling pages from watchlist after import

 * if the page to send a "remove me" does not exist, do not show it
   in the list of watched items
XWIKI-8265: Can't delete dangling pages from watchlist after import

 * some (old?) watchlists might start with comma
   fix exception thrown when feeding such a string to #unescapeList
Merge remote-tracking branch 'origin/master'