contrib/lisp/ox-rss.el (org-rss-headline): Handle empty date

* contrib/lisp/ox-rss.el (org-rss-headline): Handle empty date.

TINYCHANGE
Reported-by: "Dr. Arne Babenhauserheide" <arne_bab@web.de>
Link: https://orgmode.org/list/875z49echi.fsf@web.de/

contrib/lisp/ox-rss.el

@@ -245,7 +245,7 @@ communication channel."
 			(or (org-element-property :CATEGORY headline) "") info))
 	     (pubdate0 (org-element-property :PUBDATE headline))
 	     (pubdate (let ((system-time-locale "C"))
-			(if pubdate0
+			(if (and pubdate0 (not (string-empty-p pubdate0)))
 			    (format-time-string
 			     "%a, %d %b %Y %H:%M:%S %z"
 			     (org-time-string-to-time pubdate0)))))
@@ -270,7 +270,7 @@ communication channel."
 			  (org-element-property :CUSTOM_ID headline)
 			  publink)
 		      info))))
-	(if (not pubdate0) "" ;; Skip entries with no PUBDATE prop
+	(if (not pubdate) "" ;; Skip entries with no PUBDATE prop
 	  (format
 	   (concat
 	    "<item>\n"