Protected linebreak element after timestamp markup

* org-html.el (org-html-handle-time-stamps): Protected linebreak
element after timestamp markup.

Follow up of 1fb33b595daf4ae1fe5701beb6d5b54f8309f2f8.

lisp/org-html.el

@@ -2155,7 +2155,7 @@ But it has the disadvantage, that Org-mode's HTML conversions cannot be used."
 	  s
 	(setq r (concat r s))
 	(unless (string-match "\\S-" (concat b s))
-	  (setq r (concat r "<br/>")))
+	  (setq r (concat r "@<br/>")))
 	r))))
 
 (defvar htmlize-buffer-places)  ; from htmlize.el