mu4e: Added workaround for #417.

mu4e/mu4e-view.el

@@ -175,6 +175,8 @@ messages - for example, `mu4e-org'."
   ;; not, when the policy is 'ask'. we simply assume the user said yes...  the
   ;; alternative would be to ask for each message, encrypted or not.  maybe we
   ;; need an extra policy...
+  (if-let ((view-buffer (get-buffer "*mu4e-view*")))
+			(kill-buffer view-buffer))
   (mu4e~proc-view msgid mu4e-view-show-images mu4e-decryption-policy))
 
 (defun mu4e~view-custom-field (msg field)