org-element: Fix void-function org-clocking-buffer error

* lisp/org-element.el (org-element-headline-parser,
  org-element-inlinetask-parser): Fix void-function
  org-clocking-buffer error.

lisp/org-element.el

@@ -798,7 +798,8 @@ Assume point is at beginning of the headline."
 				     (skip-chars-backward " \r\t\n")
 				     (forward-line)
 				     (point))))
-	   (clockedp (and (eq (org-clocking-buffer)
+	   (clockedp (and (featurep 'org-clock)
+			  (eq (org-clocking-buffer)
 			      (or (buffer-base-buffer) (current-buffer)))
 			  (save-excursion
 			    (goto-char (marker-position org-clock-marker))
@@ -966,7 +967,8 @@ Assume point is at beginning of the inline task."
 		       (end-of-line)
 		       (and (re-search-forward "^\\*+ END" limit t)
 			    (match-beginning 0))))
-	   (clockedp (and (eq (org-clocking-buffer)
+	   (clockedp (and (featurep 'org-clock)
+			  (eq (org-clocking-buffer)
 			      (or (buffer-base-buffer) (current-buffer)))
 			  (let ((clock (marker-position org-clock-marker)))
 			    (and (> clock begin) (< clock task-end)))))