Fix issue reported by FireFart

Author: itsecurityco

modules/exploits/multi/http/mantisbt_php_exec.rb

@@ -89,7 +89,7 @@ def do_login()
 
     unless res.redirection.to_s !~ /login_page.php/
       print_error("Wrong credentials")
-      return false
+      fail_with(Failure::NoAccess)
     end
 
     @cookies = "#{ @cookies } #{ res.get_cookies }"