handle a blank response body

sometimes the response body itself can be blank
so we need to handle that properly.

MSP-9972

Author: David Maloney

lib/rex/parser/appscan_nokogiri.rb

@@ -195,6 +195,9 @@ def record_request_and_response
       res_header = Rex::Proto::Http::Packet::Header.new
       req_header.from_s request_headers.lstrip
       res_header.from_s response_headers.lstrip
+      if response_body.blank?
+        response_body = ''
+      end
       @state[:request_headers] = req_header
       @state[:request_body] = request_body.lstrip
       @state[:response_headers] = res_header