Check with "--one-way" flag should not traverses all destination directories

(I am not entirely sure whether this should be a feature request or be considered a bug/issue)

I have several directories in my source, let's call them b/ and d/, the destination (remote) has the directories a/, b/,c/, and d/.

Currently when running rclone check --one-way src: dest: rclone will also retrieve the contents of a/ and c/ on the destination despite them not being present in the source and thus irrelevant for a one-way check.

This is somehat of an issue because it can slow the process down significantly if many files and subdirectories are present in those paths as well as incur additional costs with remotes such as Backblaze B2 that charge for API requests past a certain limit.

I believe operations such as "copy" already only traverse directories that are present in both, so that behaviour should be mirrored here.

I think this is a missed optimization opportunity.

Luckily it is is extremely easy to add!

Try this (uploaded in 15-30 mins)

Works great :+1:
With the test build my test finished in 12 seconds, whereas the stable release version sits idle because it's being rate limited.

Thanks for testing

I've merged this to master now which means it will be in the latest beta in 15-30 mins and released in v1.51