org-agenda: Fix "no-catch --cl-block-nil--"

* lisp/org-agenda.el (org-agenda-get-category-icon): Use `cl-dolist'
  instead of `dolist'.

Reported-by: Karl Voit <devnull@Karl-Voit.at>
<http://permalink.gmane.org/gmane.emacs.orgmode/110443>

lisp/org-agenda.el

@@ -6447,7 +6447,7 @@ The flag is set if the currently compiled format contains a `%b'.")
 
 (defun org-agenda-get-category-icon (category)
   "Return an image for CATEGORY according to `org-agenda-category-icon-alist'."
-  (dolist (entry org-agenda-category-icon-alist)
+  (cl-dolist (entry org-agenda-category-icon-alist)
     (when (string-match-p (car entry) category)
       (if (listp (cadr entry))
 	  (cl-return (cadr entry))