OnFailure resolving can trigger infinite loop

It is possible to create an infinite loop in the systemd resolver for the OnFailure unit.

This can be reproduced by running the following script in a login session:

mkdir -p ~/.config/systemd/user
cd ~/.config/systemd/user

cat >a.target <<%EOF
[Unit]
OnFailure=b.target
Requisite=d.target
%EOF

cat >b.target <<%EOF
[Unit]
Requires=c.target
%EOF

cat >c.target <<%EOF
[Unit]
Wants=a.target
%EOF

cat >d.target <<%EOF
[Unit]
%EOF

journalctl -f &
systemctl --user daemon-reload
systemctl --user start c.target &
sleep 1
killall -9 systemd

This results in a lot of messages like:

Apr 19 21:10:42 ben-x1 systemd[13163]: Dependency failed for a.target.
Apr 19 21:10:42 ben-x1 systemd[13163]: Dependency failed for a.target.
Apr 19 21:10:42 ben-x1 systemd[13163]: a.target: Job a.target/start failed with result 'dependency'.
Apr 19 21:10:42 ben-x1 systemd[13163]: a.target: Job a.target/start failed with result 'dependency'.
Apr 19 21:10:42 ben-x1 systemd[13163]: a.target: Triggering OnFailure= dependencies.
Apr 19 21:10:42 ben-x1 systemd[13163]: a.target: Triggering OnFailure= dependencies.

Reproduce the loop with the unit files and commands in the issue, then watch the repeated messages with journalctl while starting c.target through systemctl --user. Trace the systemd dependency and OnFailure resolution involved in the reproduction. Done means the same unit graph no longer produces unbounded repeated failure and OnFailure messages.