emacs: Drop content-free "Unknown signature status" button

When we have not been able to evaluate the signature status of a given
MIME part, showing a content-free (and interaction-free) "[ Unknown
signature status ]" button doesn't really help the user at all, and
takes up valuable screen real-estate.

A visual reminder that a given message is *not* signed isn't helpful
unless it is always present, in which case we'd want to see "[ Unknown
signature status ]" buttons on all messages, even ones that don't have
a signing structure, but i don't think we want that.

Amended by db to drop the unused initialization of 'label'

emacs/notmuch-crypto.el

@@ -93,7 +93,8 @@ mode."
 (defun notmuch-crypto-insert-sigstatus-button (sigstatus from)
   (let* ((status (plist-get sigstatus :status))
 	 (help-msg nil)
-	 (label "Signature not processed")
+	 (show-button t)
+	 (label nil)
 	 (face 'notmuch-crypto-signature-unknown)
 	 (button-action (lambda (button) (message (button-get button 'help-echo)))))
     (cond
@@ -118,9 +119,11 @@ mode."
       (let ((keyid (concat "0x" (plist-get sigstatus :keyid))))
 	(setq label (concat "Bad signature (claimed key ID " keyid ")"))
 	(setq face 'notmuch-crypto-signature-bad)))
+     (status
+      (setq label (concat "Unknown signature status: " status)))
      (t
-      (setq label (concat "Unknown signature status"
+      (setq show-button nil)))
-			  (if status (concat ": " status))))))
+    (when show-button
       (insert-button
        (concat "[ " label " ]")
        :type 'notmuch-crypto-status-button-type
@@ -130,7 +133,7 @@ mode."
        'action button-action
        :notmuch-sigstatus sigstatus
        :notmuch-from from)
-    (insert "\n")))
+      (insert "\n"))))
 
 (declare-function notmuch-show-refresh-view "notmuch-show" (&optional reset-state))
 

test/emacs-show.expected-output/notmuch-show-decrypted-message

@@ -5,7 +5,6 @@ Date: Sat, 01 Jan 2000 12:00:00 +0000
 
 [ multipart/encrypted ]
 [ Decryption successful ]
-[ Unknown signature status ]
 [ application/pgp-encrypted ]
 [ text/plain ]
 The password is "abcd1234!", please do not tell anyone.

test/emacs-show.expected-output/notmuch-show-decrypted-message-no-crypto

@@ -5,6 +5,5 @@ Date: Sat, 01 Jan 2000 12:00:00 +0000
 
 [ multipart/encrypted ]
 [ Unknown encryption status ]
-[ Unknown signature status ]
 [ application/pgp-encrypted ]
 [ application/octet-stream ]

test/emacs-show.expected-output/notmuch-show-process-crypto-mime-parts-off

@@ -9,7 +9,6 @@ Subject: [notmuch] Working with Maildir storage?
 
   [ multipart/mixed ]
   [ multipart/signed ]
-  [ Unknown signature status ]
   [ text/plain ]
   > See the patch just posted here.
 

test/emacs-show.expected-output/notmuch-show-undecryptable-message

@@ -5,6 +5,5 @@ Date: Thu, 22 Dec 2016 08:34:56 -0400
 
 [ multipart/encrypted ]
 [ Decryption error ]
-[ Unknown signature status ]
 [ application/pgp-encrypted ]
 [ application/octet-stream ]