Avoid synchronizing files that are already in sync.

[JohnTheGr8]

What happens

When checking through the local files for the first time, any files that exist on both sides (client and server) will be re-uploaded and overwritten on the server side, even if the files were identical in the first place.

What should happen

If the remote file appears to be identical to the local one (size comparison, since we can't rely on hash comparison), synchronization should be skipped and the file should be marked as synced.