Previously when cancelling a copy the ioslave would continue.
The file copy job would then remove the file.
The dest file being removed would cause an IO error in the slave resulting in warnings such as :
kf5.kio.kio_file: Could not change permissions for "... kf5.kio.kio_file: Couldn't preserve group for "... kf5.kio.kio_file: Couldn't preserve access and modification time for "...
Preserve clean up of intermediate file copy leftover.