use get_emailuser_with_import when check if user exists (#4787)
use get_emailuser_with_import when check if user exists (#4787)

Co-authored-by: lian <e6f14efef9fae0ae8f92d04007faea68035873ce@seafile.com>
miurahr/seahub,miurahr/seahub,miurahr/seahub,miurahr/seahub