org-element--current-element: Use explicit regexp to match headline

* lisp/org-element.el (org-element--current-element): Do not call
`org-at-heading-p' to determine if we are at headline element.
`org-at-heading-p' calls `beginning-of-line' and may match
non-headlines as headlines.

lisp/org-element.el

@@ -4191,7 +4191,7 @@ element it has to parse."
             ;; Node Property.
             ((eq mode 'node-property) (org-element-node-property-parser limit))
             ;; Headline.
-            ((org-with-limited-levels (org-at-heading-p))
+            ((org-with-limited-levels (looking-at-p org-outline-regexp-bol))
              (org-element-headline-parser limit raw-secondary-p))
             ;; Sections (must be checked after headline).
             ((eq mode 'section) (org-element-section-parser limit))