Fix "(wrong-number-of-arguments max 0)" with fast tag selection

* lisp/org.el (org-fast-tag-selection): Fix
  "(wrong-number-of-arguments max 0)" error when setting tag and no
  tag is defined.

lisp/org.el

@@ -15090,10 +15090,12 @@ TODO keywords, should these have keys assigned to them.
 If the keys are nil, a-z are automatically assigned.
 Returns the new tags string, or nil to not change the current settings."
   (let* ((fulltable (append table todo-table))
-	 (maxlen (apply 'max (mapcar
-			      (lambda (x)
-				(if (stringp (car x)) (string-width (car x)) 0))
-			      fulltable)))
+	 (maxlen (if (null fulltable) 0
+		   (apply #'max
+			  (mapcar (lambda (x)
+				    (if (stringp (car x)) (string-width (car x))
+				      0))
+				  fulltable))))
 	 (buf (current-buffer))
 	 (expert (eq org-fast-tag-selection-single-key 'expert))
 	 (buffer-tags nil)