Enhancement: Don't abort sync if a user requests a file

Previously we aborted any running sync if a user requested a file that was not yet available locally.
This was done to ensure the user does not need to wait for the current sync to finish.
However, in today's code both actions the download and the sync can run in parallel.

https://github.com/owncloud/client/pull/9956
https://github.com/owncloud/client/issues/9832
