acl_parsing: Avoid NULL dereference
acl_parsing: Avoid NULL dereference

As revealed by Coverity scan report:

https://bugzilla.redhat.com/show_bug.cgi?id=728245#c8
https://bugzilla.redhat.com/attachment.cgi?id=530435

Error: REVERSE_INULL:
acl_parsing.c:172: deref_ptr: Directly dereferencing pointer "filters".
acl_parsing.c:174: check_after_deref: Dereferencing "filters" before a null
                   check.

Signed-off-by: Eduardo Lima (Etrunko) <62d34c03f1c79cee129ea3245d580303ab09f27f@br.ibm.com>

libvirt/libvirt-cim,libvirt/libvirt-cim,libvirt/libvirt-cim