fix per wchen

Author: h00die

modules/exploits/linux/http/tiki_calendar_exec.rb

@@ -85,7 +85,7 @@ def authenticate
       # double check auth worked and we got a Log out on the page.
       # at times I got it to auth, but then it would give permission errors
       # so we want to try to double check everything is good
-      unless res.body =~ /Log out/
+      if res && !res.body =~ /Log out/
         fail_with(Failure::UnexpectedReply, "#{peer} Login Failed with #{datastore['USERNAME']}:#{datastore['PASSWORD']}")
       end
       vprint_good("Login Successful!")