Check DB is active before querying sessions

lib/msf/base/serializer/readable_text.rb

@@ -620,12 +620,14 @@ class ReadableText
           'Indent' => indent,
           'SortIndex' => 1)
 
+      if framework.db.active
         framework.db.sessions.each do |session|
           unless session.closed_at.nil?
             row = create_mdm_session_row(session, show_extended)
             tbl << row
           end
         end
+      end
 
       output << (tbl.rows.count > 0 ? tbl.to_s : "#{tbl.header_to_s}No inactive sessions.\n")
     end