Third fix for the time-grid problem.

Hopefully the last one.  See commit 7b188f7d.
Reported by Memnon Anon <gegendosenfleisch@googlemail.com>.

lisp/org-agenda.el

@@ -5117,7 +5117,7 @@ The modified list may contain inherited tags, and tags matched by
 	  (throw 'exit list))
       (while (setq time (pop gridtimes))
 	(unless (and remove (member time have))
-	  (setq time (format "%4d" time))
+	  (setq time (replace-regexp-in-string " " "0" (format "%4s" time)))
 	  (push (org-format-agenda-item
 		 nil string "" nil
 		 (concat (substring time 0 -2) ":" (substring time -2)))