Lists: Avoid unnecessary buffer-modified

When fixing bullet types, bullets are now only replaced if they would
change, so if nothing changes, the buffer will remain unmodified.

lisp/ChangeLog

@@ -2,6 +2,7 @@
 
 	* org-list.el (org-toggle-checkbox): Make double prefix set the
 	checkbox to "[-]".
+	(org-fix-bullet-type): Only replace bullet it it is changed.
 
 	* org.el (org-add-log-setup): Fix positioning when
 	`org-log-states-order-reversed' is nil.

lisp/org-list.el

@@ -761,7 +761,7 @@ Also, fix the indentation."
 	  (skip-chars-forward " \t")
 	  (looking-at "\\S-+ *")
 	  (setq oldbullet (match-string 0))
-	  (replace-match bullet)
+	  (unless (equal bullet oldbullet) (replace-match bullet))
 	  (org-shift-item-indentation (- (length bullet) (length oldbullet))))))
     (goto-line line)
     (org-move-to-column col)