emacs: Fix 'guix-pull'.

* emacs/guix-base.el (guix-pull): Handle prefix argument when it is run
  interactively.  Use 'guix-command' instead of 'guix-pull' to prevent
  REPL exit if 'leave' happens.

emacs/guix-base.el

@@ -1186,10 +1186,11 @@ The function is called with a single argument - a command line string."
 (defun guix-pull (&optional verbose)
   "Run Guix pull operation.
 If VERBOSE is non-nil (with prefix argument), produce verbose output."
-  (interactive)
+  (interactive "P")
   (let ((args (and verbose '("--verbose"))))
     (guix-eval-in-repl
-     (apply #'guix-make-guile-expression 'guix-pull args)
+     (apply #'guix-make-guile-expression
+            'guix-command "pull" args)
      nil 'pull)))
 
 (provide 'guix-base)