state diff might be lost after state update in enclave

[haerdib]

Currently the state of the enclave is updated and then the sidechainblock, which contains the state diff, is sent to the worker which then stores the block whitin is db and broadcasts it.

Problem: when en error occurs (e.g. blackout) after the enclave state update and before the worker db storage, the block containing the state diff will be lost.

Solution proposal: update the enclave state with the state diff of its own produced block from the previous interval.

Careful: do not mix up states - the first thing that needs to be done before processing any trusted calls, the state must be updated.

[brenzi]

connected to #345

[haerdib]

Current status: We only update the state after broadcasting, so that should not be an issue any more. What needs to be checked before finally closing this issue: when is the sidechain block db updated? Is there a possible discrepancy?