Update documentation and add check before exploit

documentation/modules/exploit/windows/http/manageengine_appmanager_exec.md

@@ -4,7 +4,7 @@ This module exploits command injection vulnerability in the ManageEngine Applica
 **Vulnerable Application Installation Steps**
 
 Go to following website and download Windows version of the product. It comes with built-in Java and Postgresql so you don't need to install anything else.
-[https://www.manageengine.com/products/applications_manager/download.html](https://www.manageengine.com/products/applications_manager/download.html)
+[http://archives.manageengine.com/applications_manager/13630/](http://archives.manageengine.com/applications_manager/13630/)
 
 ## Verification Steps
 

modules/exploits/windows/http/manageengine_appmanager_exec.rb

@@ -65,6 +65,8 @@ class MetasploitModule < Msf::Exploit::Remote
   end
 
   def exploit
+    fail_with(Failure::NotVulnerable, 'Target is not vulnerable.') unless check == Exploit::CheckCode::Vulnerable
+
     powershell_options = {
       encode_final_payload: true,
       remove_comspec: true