nnimap `never' expiration fix

* nnimap.el (nnimap-find-expired-articles): Fix handling of
(expiry-wait . never).

lisp/gnus/ChangeLog

+2015-01-28  Elias Oltmanns  <eo@nebensachen.de>
+
+	* nnimap.el (nnimap-find-expired-articles): Fix handling of
+	(expiry-wait . never).
+
 2015-01-27  Lars Ingebrigtsen  <larsi@gnus.org>
 	* nnir.el (nnir-imap-expr-to-imap): Check for literal+ capability in

lisp/gnus/nnimap.el

@@ -1020,20 +1020,20 @@ textual parts.")
 
 (defun nnimap-find-expired-articles (group)
   (let ((cutoff (nnmail-expired-article-p group nil nil)))
-    (with-current-buffer (nnimap-buffer)
-      (let ((result
-	     (nnimap-command
-	      "UID SEARCH SENTBEFORE %s"
-	      (format-time-string
-	       (format "%%d-%s-%%Y"
-		       (upcase
-			(car (rassoc (nth 4 (decode-time cutoff))
-				     parse-time-months))))
-	       cutoff))))
-	(and (car result)
-	     (delete 0 (mapcar #'string-to-number
-			       (cdr (assoc "SEARCH" (cdr result))))))))))
-
+    (when cutoff
+      (with-current-buffer (nnimap-buffer)
+	(let ((result
+	       (nnimap-command
+		"UID SEARCH SENTBEFORE %s"
+		(format-time-string
+		 (format "%%d-%s-%%Y"
+			 (upcase
+			  (car (rassoc (nth 4 (decode-time cutoff))
+				       parse-time-months))))
+		 cutoff))))
+	  (and (car result)
+	       (delete 0 (mapcar #'string-to-number
+				 (cdr (assoc "SEARCH" (cdr result)))))))))))
 
 (defun nnimap-find-article-by-message-id (group server message-id
 						&optional limit)