ox: Fix "wrong-type-argument" error in template insertion

* lisp/ox.el (org-export-insert-default-template): Fix
  "wrong-type-argument" error in template insertion.

Thanks to Eric Abrahamsen for reporting this.

lisp/ox.el

@@ -3182,7 +3182,7 @@ locally for the subtree through node properties."
 			 ((org-export-backend-p backend)
 			  (org-export-get-all-options backend))
 			 (t (org-export-get-all-options
-			     (org-export-backend-name backend)))))
+			     (org-export-get-backend backend)))))
       (let ((keyword (nth 1 entry))
             (option (nth 2 entry)))
         (cond