New code from rBd05909a70c36 last week did not take into account
liboverride templates and `NOOP` operations. So we cannot assume that
there is no valid override property for these which need to be restored.
While we may get rid of templates at some point now, for now they are
still exposed in PY API, and have some basic unittests, so keep them
working as best as possible.
Issue reported on IRC by Martijn Versteegh (@Baardaap), thanks!
a6b6f5db10