Don't perform current user ops in switch_to_blog() or restore_current_blog()...

Don't perform current user ops in switch_to_blog() or restore_current_blog() if init hasn't fired. Avoids wp_get_current_user() not defined error when those functions are run before init.  Ops on current user prior to init are meaningless anyway. see #13934

git-svn-id: https://core.svn.wordpress.org/trunk@15331 1a063a9b-81f0-0310-95a4-ce76da25c4cd