fix(global_defaults): handle disks without mount key in mountpoint validation

roles/global_defaults/tasks/validation.yml

@@ -310,8 +310,8 @@
     system_disk_mounts: >-
       {{
         (system_cfg.disks | default([]))
-        | map(attribute='mount')
-        | map(attribute='path')
+        | map(attribute='mount', default={})
+        | map(attribute='path', default='')
         | map('string')
         | map('trim')
         | reject('equalto', '')