Bug: Fixed conversation reply mail issue when an attachment is sent (#655)

* When an attachment was sent in the reply mailer it was breaking due to the
truncating function applied on the last message content. Here the content was empty
and so it broke.
* Fixed this breakage
* Also addressed the issue that if the attachment was there the content was coming empty.
With these changes, made the content to have a link to the attachment.

app/mailers/conversation_reply_mailer.rb

@@ -20,7 +20,8 @@ class ConversationReplyMailer < ApplicationMailer
 
   private
 
-  def mail_subject(last_message, trim_length = 30)
-    "[##{@conversation.display_id}] #{last_message.content.truncate(trim_length)}"
+  def mail_subject(last_message, trim_length = 50)
+    subject_line = last_message&.content&.truncate(trim_length) || 'New messages on this conversation'
+    "[##{@conversation.display_id}] #{subject_line}"
   end
 end

app/views/mailers/conversation_reply_mailer/reply_with_summary.html.erb

@@ -8,7 +8,13 @@
       <td>
         <b><%= message.incoming? ? 'You' : message.user.name %></b>
       </td>
-      <td>: <%= message.content %></td>
+      <td>:
+        <% if message.attachment %>
+          attachment [<a href="<%= message.attachment.file_url %>" _target="blank">click here to view</a>]
+        <% else %>
+          <%= message.content %>
+        <% end %>
+      </td>
     </tr>
   <% end %>
 </table>