fix sent invitations screen

Avoiding the PHP warning in 19b065ca8e4838658a83eb98da4f761f5cb08a6f has accidentally broken the "Sent Invitations" list, because `invite_anyone_setup_globals()` runs after `Invite_Anyone_Schema::register_post_type()` on `invite_anyone_screen_two()` and inadvertently clears `$bp->invite_anyone->invitee_tax_name` and `$bp->invite_anyone->invited_groups_tax_name`.