ob-core: Fix infloop when filling a region with a source block

* lisp/ob-core.el (org-babel-do-in-edit-buffer): Do not move point.

Reported-by: Yasushi SHOJI <yasushi.shoji@gmail.com>
<http://lists.gnu.org/r/emacs-orgmode/2018-02/msg00006.html>

lisp/ob-core.el

@@ -980,13 +980,24 @@ with a prefix argument then this is passed on to
 (defmacro org-babel-do-in-edit-buffer (&rest body)
   "Evaluate BODY in edit buffer if there is a code block at point.
 Return t if a code block was found at point, nil otherwise."
-  `(let ((org-src-window-setup 'switch-invisibly))
-     (when (and (org-babel-where-is-src-block-head)
+  (declare (debug (body)))
+  `(let* ((element (org-element-at-point))
+	  ;; This function is not supposed to move point.  However,
+	  ;; `org-edit-src-code' always moves point back into the
+	  ;; source block.  It is problematic if the point was before
+	  ;; the code, e.g., on block's opening line.  In this case,
+	  ;; we want to restore this location after executing BODY.
+	  (outside-position
+	   (and (<= (line-beginning-position)
+		    (org-element-property :post-affiliated element))
+		(point-marker)))
+	  (org-src-window-setup 'switch-invisibly))
+     (when (and (org-babel-where-is-src-block-head element)
 		(org-edit-src-code))
        (unwind-protect (progn ,@body)
-	 (org-edit-src-exit))
+	 (org-edit-src-exit)
+	 (when outside-position (goto-char outside-position)))
        t)))
-(def-edebug-spec org-babel-do-in-edit-buffer (body))
 
 (defun org-babel-do-key-sequence-in-edit-buffer (key)
   "Read key sequence and execute the command in edit buffer.