b2: Fix SHA1 mismatch when downloading files with no SHA1 #678
b2: Fix SHA1 mismatch when downloading files with no SHA1 #678

Some large files (depending on which version of rclone they were
uploaded with and where they were uploaded from) don't have an SHA1,
so we can't check it in that case.

yonjah/rclone,B4dM4n/rclone,yonjah/rclone,olihey/rclone,yonjah/rclone,B4dM4n/rclone,B4dM4n/rclone,seuffert/rclone,seuffert/rclone,ncw/rclone,olihey/rclone,olihey/rclone,olihey/rclone,seuffert/rclone,ncw/rclone,seuffert/rclone,yonjah/rclone,B4dM4n/rclone,ncw/rclone,ncw/rclone