Otherwise, ReadOnly DBus property in org.freedesktop.machine1.Image or
org.freedesktop.portable1.Image will not be updated by MarkReadOnly DBus
method.

Same as the previous commit, but for SetLimit DBus method vs Limit
property and friends.

Preparation for the next commit. No functional change.

…he main interface is called

Previously, Image objects were only cached when reading properties or
methods in the org.freedesktop.machine1.Image interface are called.

This makes that, when a method in the main interface (org.freedesktop.machine1)
for an image is called, also acquire the Image object from the cache,
and if not cached, create Image object and put into the cache, like we
do for org.freedesktop.machine1.Image.

Otherwise, if some properties of an image are updated by methods in the main
interface, e.g. MarkImageReadOnly(), the changes do not applied to the cached
Image object, and subsequent read of proerties through the interface for the
image, e.g. ReadOnly property, may provide outdated values.

Follow-up for 1ddb263.

Fixes systemd#32888.

Fixes a bug introduced by 1ddb263.

Note, this requires the previous two commits, and cannot backport without them.

Note, before the previous commit, the use-after-free could be triggered
only by Rename() DBus method, and could not by RenameImage(), as we did not
cache Image object when RenameImage() method is called. And machinectl
always uses RenameImage(). Hence, the issue could be triggered only when
Rename() DBus method is explicitly called by e.g. busctl.

With the previous commit, the Image object passed to the function is
always cached. Hence, the issue could be triggered even with machinectl
command, and this fix is important.