If the destination file does not exist the stat call to check the file
type fails. Extend the check of the stat return value.
To allow to copy files to a new destination.

Fixes commit 0ec6bd3e1be8 ("libfile: copy_file: Only open
regular files with O_TRUNC")

Signed-off-by: Teresa Remmet <t.remmet@phytec.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>