fix missing global-persp-mode 

this fixes the ``persp-names: Wrong type argument: hash-table-p, nil`` error for me when I call ``persp-switch`` in a fresh emacs instance (to turn persp-mode on i use the following code in my init.el

```lisp
(add-hook 'after-init-hook #'persp-mode 1)
```

This PR fixes the wrong type argument error but switching perspectives still does not work, i.e., I can now enter a name of a perspective in ``persp-switch`` but it does not switch it (``persp-last`` stays the same)

Any ideas?
(BTW: If I put (persp 1) in my init.el everything works, but I would like to use the after-init-hook)