lisp/org.el (org-sort-entries): Fix when end of region is not a bol

* lisp/org.el (org-sort-entries): Avoid putting a heading not at bol
when end of selected region is not at bol.

Reported-by: Zelphir Kaltstahl <zelphirkaltstahl@posteo.de>
Link: https://orgmode.org/list/8d637a8a-6cbc-4158-bded-f9182716a1fc@posteo.de

lisp/org.el

@@ -7778,6 +7778,12 @@ function is being called interactively."
 
     (save-restriction
       (narrow-to-region start end)
+      ;; No trailing newline - add one to avoid
+      ;; * heading
+      ;; text* another heading
+      (save-excursion
+        (goto-char end)
+        (unless (bolp) (insert "\n")))
       (let ((restore-clock?
 	     ;; The clock marker is lost when using `sort-subr'; mark
 	     ;; the clock with temporary `:org-clock-marker-backup'