lisp/org.el: Fix inserting a heading before the first entry

* lisp/org.el (org-insert-heading): When inserting a headline
before the first one, insert a blank line after the inserted
heading if the previous call to `org--blank-before-heading-p'
returned `t'.

Reported-by: Gustavo Barros <gusbrs.2016@gmail.com>
Link: https://orgmode.org/list/87y2cxoybz.fsf@gmail.com/

lisp/org.el

@@ -6959,6 +6959,11 @@ unconditionally."
 	 (when (equal arg '(16)) (org-up-heading-safe))
 	 (org-end-of-subtree)))
       (unless (bolp) (insert "\n"))
+      (when (and blank? (save-excursion
+                          (backward-char)
+                          (org-before-first-heading-p)))
+        (insert "\n")
+        (backward-char))
       (unless level (backward-char))
       (unless (and blank? (org-previous-line-empty-p))
 	(org-N-empty-lines-before-current (if blank? 1 0)))