RSVP page tokens aren't properly set

The tokens on the RSVP response form aren't being properly set. Specifically the user related tokens. When a user comes to visit the rsvp page the tokens are rendered, but using the "global $user" variable in node_invite_token_values().

The tokens need to be set similarly in the rsvp form as they are in the send form. Attached is a patch that should fix the issue.