Fix #5766, check res for send_request_raw

Fix #5766

modules/auxiliary/scanner/http/ms15_034_http_sys_memory_dump.rb

@@ -88,6 +88,11 @@ class Metasploit3 < Msf::Auxiliary
         }
       )
 
+      unless res
+        vprint_error("#{peer} - Timed out :-(")
+        return Exploit::CheckCode::Unknown
+      end
+
       vmessage = "#{peer} - Checking #{uri} [#{res.code}]"
 
       if res && res.body.include?('Requested Range Not Satisfiable')