org-indent-mode: Fix problem with empty string as line-prefix

lisp/ChangeLog

@@ -1,5 +1,8 @@
 2009-11-20  Carsten Dominik  <carsten.dominik@gmail.com>
 
+	* org-indent.el (org-indent-initialize): Avoid empty strings as
+	line prefixes.
+
 	* org-agenda.el (org-agenda-diary-entry-in-org-file): Make sure
 	hat checking for the mark does not throw an error.
 	(org-agenda-diary-entry-in-org-file): Catch the case that there is

lisp/org-indent.el

@@ -106,8 +106,8 @@ this variable can be set to nil to get rid of the timer."
   ;; Initialize the indentation and star vectors
   (setq org-indent-strings (make-vector (1+ org-indent-max) nil))
   (setq org-indent-stars (make-vector (1+ org-indent-max) nil))
-  (aset org-indent-strings 0 "")
-  (aset org-indent-stars 0 "")
+  (aset org-indent-strings 0 nil)
+  (aset org-indent-stars 0 nil)
   (loop for i from 1 to org-indent-max do
 	(aset org-indent-strings i
 	      (org-add-props