Don't show total size, number and time values of file operation

...if directory scanning was skipped before.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Avoid g_return_* macros in file operation routines

...since they produce warnings about non-created UI and clutters screen
up.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>