Bug 24522: Show alert when trying to add nothing to a list in staff

Bug 24522: Show alert when trying to add nothing to a list in staff

This patch modifies the JavaScript which handles the process of adding
items to a list in the staff client. Error-handling is added in the case
when a set of biblionumbers hasn't been passed to the vShelf function.

To test, apply the patch and perform a catalog search in the staff
client.

On the search results page, select any list from the "Add to list" menu
at the top of the search results table without checking any checkboxes.

You should get an alert, "No item was selected."

Also test that adding to a list works correctly after selecting one or
more titles.

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>