Before this change rclone would emit the message
--checksum is in use but the source and destination have no hashes in common; falling back to --size-only
When the source or destination hash was missing as well as when the
source and destination had no hashes in common.
This first case is very confusing for users when the source and
destination do have a hash in common.
This change fixes that and makes sure the error message is not emitted
on missing hashes even when there is a hash in common.
See: https://forum.rclone.org/t/source-and-destination-have-no-hashes-in-common-for-unencrypted-drive-to-local-sync/19531
20b00db390