posix_acls: clarify loop condition code, removing unneeded counter variable.

posix_acls: clarify loop condition code, removing unneeded counter variable.

Coverity ID 545 falsely classified this as a NULL dereferencing bug.
By putting the loop of walking the list of aces more naturely not using
additional counters, it becomes much more obvious that it is not entered
when dir_ace == NULL.

The same modifications are done for the file_ace loop.

Michael
(This used to be commit 6dab6cf0647d7db01e5e472f8b5cf21395b7dbf0)