org-at-heading-p: Accept optional argument

* lisp/org.el (org-at-heading-p): Use second argument to allow
checking for visible headings.  Note that by default, unlike
`outline-on-heading-p', `org-at-heading-p' returns non-nil for
invisible headings. Passing second argument is just like
`(outline-on-heading-p)'.
(org-indent-line):
* lisp/org-agenda.el (org-agenda-add-entry-to-org-agenda-diary-file):
* lisp/org-colview.el (org-columns--call):
(org-columns-store-format): Update arguments in `org-at-heading-p'
calls.

lisp/org-agenda.el

@@ -10524,7 +10524,7 @@ the resulting entry will not be shown.  When TEXT is empty, switch to
       (anniversary
        (or (re-search-forward "^\\*[ \t]+Anniversaries" nil t)
 	   (progn
-	     (or (org-at-heading-p t)
+	     (or (org-at-heading-p)
 		 (progn
 		   (outline-next-heading)
 		   (insert "* Anniversaries\n\n")

lisp/org-colview.el

@@ -699,7 +699,7 @@ FUN is a function called with no argument."
   (let ((hide-body (and (/= (line-end-position) (point-max))
 			(save-excursion
 			  (move-beginning-of-line 2)
-			  (org-at-heading-p t)))))
+			  (org-at-heading-p)))))
     (unwind-protect (funcall fun)
       (when hide-body (outline-hide-entry)))))
 
@@ -1026,7 +1026,7 @@ the current buffer."
 	      ;; No COLUMNS keyword in the buffer.  Insert one at the
 	      ;; beginning, right before the first heading, if any.
 	      (goto-char (point-min))
-	      (unless (org-at-heading-p t) (outline-next-heading))
+	      (unless (org-at-heading-p) (outline-next-heading))
 	      (let ((inhibit-read-only t))
 		(insert-before-markers "#+COLUMNS: " fmt "\n"))))
 	  (setq-local org-columns-default-format fmt))))))

lisp/org.el

@@ -17260,7 +17260,7 @@ number of stars to add."
 	;; Case 1. Started at an heading: de-star headings.
 	((org-at-heading-p)
 	 (while (< (point) end)
-	   (when (org-at-heading-p t)
+	   (when (org-at-heading-p)
 	     (looking-at org-outline-regexp) (replace-match "")
 	     (setq toggled t))
 	   (forward-line)))
@@ -17862,7 +17862,7 @@ and :keyword."
 	 (p (point)) clist o)
     ;; First the large context
     (cond
-     ((org-at-heading-p t)
+     ((org-at-heading-p)
       (push (list :headline (point-at-bol) (point-at-eol)) clist)
       (when (progn
 	      (beginning-of-line 1)
@@ -19612,9 +19612,13 @@ Respect narrowing."
        (end-of-line)
        (null (re-search-backward org-outline-regexp-bol nil t))))))
 
-(defun org-at-heading-p (&optional _)
-  "Non-nil when on a headline."
-  (outline-on-heading-p t))
+(defun org-at-heading-p (&optional invisible-not-ok)
+  "Return t if point is on a (possibly invisible) heading line.
+If INVISIBLE-NOT-OK is non-nil, an invisible heading line is not ok."
+  (save-excursion
+    (beginning-of-line)
+    (and (bolp) (or (not invisible-not-ok) (not (org-fold-folded-p)))
+	 (looking-at outline-regexp))))
 
 (defun org-in-commented-heading-p (&optional no-inheritance element)
   "Non-nil if point is under a commented heading.