Fix no file in bulletin form

vendor/built_in_modules/announcement/app/views/panel/announcement/back_end/bulletins/_form_file.html.erb

@@ -2,7 +2,11 @@
   <div class="fileupload fileupload-new start-line" data-provides="fileupload">
 <% else %>
   <div class="fileupload-exist start-line">
-  <%= link_to form_file.file_identifier, form_file.file.url, {:class => 'file-link for_preview', :target => '_blank', :title => t(:view), "data-trigger" => :hover}.merge(file_picture_preview_setting(form_file.file.url)) %>
+    <% if form_file.file.blank? %>
+      <%= t(:no_file) %>
+    <% else %>
+      <%= link_to form_file.file_identifier, form_file.file.url, {:class => 'file-link for_preview', :target => '_blank', :title => t(:view), "data-trigger" => :hover}.merge(file_picture_preview_setting(form_file.file.url)) %>
+    <% end %>
 <% end %>
   <div class="input-prepend input-append">
     <% if form_file.new_record? %>