Bugfix for crash with `SPECIAL_TAU_SPIN_CORRELATIONS`

Events with partonic hadron decays involving a tau (e.g. B -> cb d tau vtau) and multiple parton interactions could trigger a core dump in the SPECIAL_TAU_SPIN_CORRELATIONS=1 treatment. This happened due to an infinite loop, which is fixed now. In addition, in events triggering a Retry_Event a minor problem with lost spin correlations is fixed.

The problem was originally introduced in !296 (merged) and a validation in one of the original setups shows that the feature is still working correctly now with multiple parton interactions enabled: