Ensure we have a slash for the root level

Need a slash to specify the root level when updating the file manager
Ignore deleting nothing & strip trailing slashes

Don't ask the user for any confirmation if there is nothing to delete.
This could occur when you select something, delete it, then try to
delete again.
We need to also strip trailing slashes for deleting files when updating
the file manager. This is much like what we needed to do with adding
files to the root of the file manager. Locations should end without a
trailing slash, but a root is a trailing slash as its only char. A regex
here solves the issue.