Don't display form if issue if closed

lib/redmine_qbo_line_items/hooks/view_hook_listener.rb

@@ -25,6 +25,7 @@ module RedmineQboLineItems
       end
 
       def view_issues_edit_notes_bottom(context = {})
+        return if context[:issue].closed?
         context[:controller].send(:render_to_string, {
           partial: 'line_items/issue_form',
             locals: {