[Gnus] Catch the invalid-operation that idna.el will issue

* lisp/gnus/gnus-art.el (gnus-use-idna):
* lisp/gnus/gnus-sum.el (gnus-summary-idna-message):
* lisp/gnus/message.el (message-use-idna):
Catch the invalid-operation that idna.el will issue.

lisp/gnus/gnus-art.el

@@ -1627,8 +1627,11 @@ It is a string, such as \"PGP\". If nil, ask user."
 
 (defvar idna-program)
 
-(defcustom gnus-use-idna (and (condition-case nil (require 'idna) (file-error))
-			      (mm-coding-system-p 'utf-8)
+(defcustom gnus-use-idna (and (mm-coding-system-p 'utf-8)
+			      (condition-case nil
+				  (require 'idna)
+				(file-error)
+				(invalid-operation))
 			      idna-program
 			      (executable-find idna-program))
   "Whether IDNA decoding of headers is used when viewing messages.

lisp/gnus/gnus-sum.el

@@ -9870,9 +9870,11 @@ invalid IDNA string (`xn--bar' is invalid).
 You must have GNU Libidn (URL `http://www.gnu.org/software/libidn/')
 installed for this command to work."
   (interactive "P")
-  (if (not (and (condition-case nil (require 'idna)
-		  (file-error))
-		(mm-coding-system-p 'utf-8)
+  (if (not (and (mm-coding-system-p 'utf-8)
+		(condition-case nil
+		    (require 'idna)
+		  (file-error)
+		  (invalid-operation))
 		(symbol-value 'idna-program)
 		(executable-find (symbol-value 'idna-program))))
       (gnus-message

lisp/gnus/message.el

@@ -1763,7 +1763,10 @@ no, only reply back to the author."
 	       (let (mucs-ignore-version-incompatibilities)
 		 (require 'un-define))
 	     (error)))
-       (condition-case nil (require 'idna) (file-error))
+       (condition-case nil
+	   (require 'idna)
+	 (file-error)
+	 (invalid-operation))
        idna-program
        (executable-find idna-program)
        (string= (idna-to-ascii "räksmörgås") "xn--rksmrgs-5wao1o")