the previous condition checked if the final target path size was >0,
which it would only be when the file already exists (i.e. overwrite) in
all other scenarios it would always be false and as such resuming wouldn't
work. what we actually want to check is whether the part file is >0 (i.e.
there's actual pending bytes to resume from).
this makes resuming work when copying remote->local
CCBUG: 417645