org-refile: Fix heading being removed when refiling into itself

* lisp/org-refile.el (org-refile): Throw an error when attempting to
refile heading into itself and the point is not at bol.
* testing/lisp/test-org.el (test-org/refile): Add tests.

Reported-by: Oliver Epper <oliver.epper@gmail.com>
Link: https://list.orgmode.org/orgmode/CAP8tsuSEScO+Q7=g7kL=9Dk-95reJvUmLoyqmJjd2-ZM6iycfA@mail.gmail.com/

lisp/org-refile.el

@@ -523,7 +523,9 @@ prefix argument (`C-u C-u C-u C-c C-w')."
 		     (if regionp
 			 (and (>= pos region-start)
 			      (<= pos region-end))
-		       (and (>= pos (point))
+		       (and (>= pos (save-excursion
+                                     (org-back-to-heading t)
+                                     (point)))
 			    (< pos (save-excursion
 				     (org-end-of-subtree t t))))))
 	    (error "Cannot refile to position inside the tree or region"))

testing/lisp/test-org.el

@@ -7050,8 +7050,20 @@ Paragraph<point>"
 ** H2\n"
     (org-test-with-temp-text-in-file "* H1
 * H2<point>"
+      (org-refile nil nil `("H1" ,(buffer-file-name) nil 1))
+      (buffer-string))))
+  ;; Throw an error when trying to refile into itself.
+  (should-error
+   (org-test-with-temp-text-in-file "* H<point>1
+* H2"
      (org-refile nil nil `("H1" ,(buffer-file-name) nil 1))
-     (buffer-string)))))
+     (buffer-string)))
+  (should-error
+   (org-test-with-temp-text-in-file "* one
+* t<point>wo
+* three"
+     (org-refile nil nil `("two" ,(buffer-file-name) nil 7))
+     (buffer-string))))
 
 
 ;;; Sparse trees