s3: Fix empty checks in auth
s3: Fix empty checks in auth

B4dM4n/rclone,yonjah/rclone,yonjah/rclone,B4dM4n/rclone,B4dM4n/rclone,jackschmidt/rclone,arcimboldo/rclone,seuffert/rclone,seuffert/rclone,ncw/rclone,jackschmidt/rclone,arcimboldo/rclone,jackschmidt/rclone,olihey/rclone,ncw/rclone,kynikos/rclone,ncw/rclone,yonjah/rclone,seuffert/rclone,arcimboldo/rclone,B4dM4n/rclone,olihey/rclone,kynikos/rclone,ncw/rclone,arcimboldo/rclone,seuffert/rclone,jackschmidt/rclone,olihey/rclone,kynikos/rclone,olihey/rclone,kynikos/rclone,yonjah/rclone