kioworker file: copy() fix posix acl copying

Reported in https://discuss.kde.org/t/dolphin-seems-not-to-respect-default-acls-on-directories/5577

Manually tested following test scenario After

getfacl  testacl/f-dolphin 
# file: testacl/f-dolphin
# owner: meven
# group: meven
user::rw-
group::rwx                      #effective:rw-
group:users:rwx                 #effective:rw-
mask::rw-
other::r--

The issue is, we try to read and write the ACL when the src and destfile are closed.

BUG: 475150