archive_write_disk_posix: fix writing fflags broken in 8a1bd5c

archive_write_disk_posix: fix writing fflags broken in 8a1bd5c

The fixup list was erroneously assumed to be directories only.
Only in the case of critical file flags modification (e.g. SF_IMMUTABLE
on BSD systems), other file types (e.g. regular files or symbolic links)
may be added to the fixup list. We still need to verify that we are writing
to the correct file type, so compare the archive entry file type with
the file type of the file to be modified.

Fixes #1617