tauMonitoring: skip taus failing AOD thinning cut

Hello,

!72397 revealed an issue in the offline tau monitoring (ATLASRECTS-8037).
We have an early stopping condition in the tau reconstruction: if the tau is too soft, it won't be written to AOD (it will be dropped by a thinning algorithm), and therefore we abort its reconstruction, e.g. we don't run tau ID.
Still, we currently try to access ID-related variables in the monitoring, and it now fails.
This MR is skipping these incompletely-built taus.

Cheers,
Bertrand