Improve error state handling in SyncedList _sync
Improve error state handling in SyncedList _sync

This helps ensure that even if we raise an error, we do so in a way that
mantains a proper state for the SyncedList object.

joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue