crypt: fix panic on close after failed seek
crypt: fix panic on close after failed seek

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