maple_tree: fix mas_empty_area_rev() null pointer dereference
JIRA: https://issues.redhat.com/browse/RHEL-39862
JIRA: https://issues.redhat.com/browse/RHEL-39863
Tested: sanity
Signed-off-by: Aristeu Rozanski arozansk@redhat.com
Edited by Aristeu Rozanski