Fix rapid7#6085, NoMethodError in vim_soap.rb

Fix rapid7#6085

Author: wchen-r7

lib/msf/core/exploit/vim_soap.rb

@@ -185,8 +185,8 @@ def vim_get_session
       'headers' => { 'SOAPAction' => @soap_action}
     }, 25)
     return false unless res and res.code == 200
-     @server_objects = Hash.from_xml(res.body)['Envelope']['Body']['RetrieveServiceContentResponse']['returnval']
-     @soap_action = "urn:vim25/#{@server_objects['about']['apiVersion']}"
+     @server_objects = (((Hash.from_xml(res.body)['Envelope'] || {})['Body'] || {})['RetrieveServiceContentResponse'] || {})['returnval']
+     @soap_action = "urn:vim25/#{(@server_objects['about'] || {})['apiVersion']}"
     if res.headers['Set-Cookie']
       @vim_cookie = res.headers['Set-Cookie']
       return true