fix: can't delete a session from Telescope picker

Sometimes deleting a session from the the Telescope picker wasn't
working. It happens when we have extra command files that are filtered
out from the list. Those files break some code in Telescope that finds
the item we want to delete in the picker results. More detail is here:

nvim-telescope/telescope.nvim#3265

We work around the issue by having the Telescope entry maker returning
{} instead of nil. That's not perfect but better than not being able to
delete/

lua/auto-session/session-lens/init.lua

@@ -20,7 +20,11 @@ function SessionLens.make_telescope_callback(opts)
     -- Don't include <session>x.vim files that nvim makes for custom user
     -- commands
     if not Lib.is_session_file(session_root_dir .. file_name) then
-      return nil
+      -- FIXME: Returning nil would be better here since otherwise the result count
+      -- will be off. However, returning nil can prevent delete from working so return {}
+      -- until this is fixed:
+      -- https://github.com/nvim-telescope/telescope.nvim/issues/3265
+      return {}
     end
 
     -- the name of the session, to be used for restoring/deleting