Fix: (--outline-path) Always return a string

org-heading-components returns nil for a heading without heading text,
which causes string-match to signal an error.  So we'll match the
regexp ourselves and return an empty string in that case.  Should be
slightly faster, anyway.

org-ql.el

@@ -429,7 +429,10 @@ Returns cons (INHERITED-TAGS . LOCAL-TAGS)."
 (defun org-ql--outline-path ()
   "Return outline path for heading at point."
   (save-excursion
-    (let ((heading (nth 4 (org-heading-components))))
+    (let ((heading (save-match-data
+                     (if (looking-at org-complex-heading-regexp)
+                         (or (match-string 4) "")
+                       ""))))
       (if (org-up-heading-safe)
           ;; MAYBE: It seems wrong to call the cache function from
           ;; inside this function, like a violation of separation of