fixup! org-fold-show-set-visibility: Do not reveal emphasis unless DETAIL is `local'

* lisp/org-fold.el (org-fold-show-set-visibility--text-properties):
Consider nil value for REGION.

lisp/org-fold.el

@@ -845,8 +845,9 @@ DETAIL is either nil, `minimal', `local', `ancestors',
                 (let (font-lock-extend-region-functions)
                   (font-lock-fontify-region (max (point-min) (1- (car region))) (cdr region))))))
           ;; Unfold links.
-          (dolist (spec '(org-link org-link-description))
-            (org-fold-region (car region) (cdr region) nil spec)))
+          (when region
+            (dolist (spec '(org-link org-link-description))
+              (org-fold-region (car region) (cdr region) nil spec))))
         (when region
           (dolist (spec (org-fold-core-folding-spec-list))
             ;; Links are taken care by above.