FIX: excerpt will not work if custom fields is nil

FIX: excerpt will not work if custom fields is nil

Follow up on 5c99fad1eb5f72cf79

diff --git a/plugin.rb b/plugin.rb
index a2f0ef2..9408d9a 100644
--- a/plugin.rb
+++ b/plugin.rb
@@ -141,9 +141,8 @@ after_initialize do
     # Patch method to hide excerpt of encrypted message (i.e. in push
     # notifications).
     def excerpt(maxlength = nil, options = {})
-      if topic.custom_fields["encrypted_title"]
+      if has_encrypted_title?
         maxlength ||= SiteSetting.post_excerpt_maxlength
-
         return I18n.t("encrypt.encrypted_excerpt")[0..maxlength]
       end

GitHub sha: 8d506a29