lib/copydir.c: copy_entry(): Use temporary stat buffer

lib/copydir.c: copy_entry(): Use temporary stat buffer

There are no guarantees that fstatat() does not clobber the stat
buffer on errors.

Use a temporary buffer so that the following code sees correct
attributes of the source entry.

Link: <https://github.com/shadow-maint/shadow/issues/973>
Signed-off-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
Reviewed-by: Alejandro Colomar <alx@kernel.org>
Cherry-picked-from: 000619344ddb ("lib/copydir:copy_entry(): use temporary stat buffer")
Link: <https://github.com/shadow-maint/shadow/pull/974>
Signed-off-by: Alejandro Colomar <alx@kernel.org>