I think that if a reorg fails due to an error while disconnecting blocks, the node should shut down.

My thought is that if we are trying to switch to a more work chain and something goes wrong before we can even try to validate that more-work chain, then we have a problem that is not related to the chain we're trying to switch to but instead related to our own hardware or software; shutting down and having the user deal with the issue is better than continuing on, when we know there's a more work chain that we're unable to try validating.

This has recently come up on testnet, where unpatched nodes are unable to reorg from the invalid chain containing the duplicate-input-in-a-transaction block, but rather than crash or shutdown they are continuing on the invalid chain, with messages like this in the debug log:

```
ERROR: DisconnectTip(): DisconnectBlock 00000000210004840364b52bc5e455d888f164e4264a4fec06a514b67e9d5722 failed
```
{
                            fReplacementOptOut = false;
                            break;
                        }
                    }
                }
                if (fReplacementOptOut) {
                    return state.Invalid(false, REJECT_DUPLICATE, "txn-mempool-conflict");
                }
                setConflicts.insert(ptxConflicting->GetHash());
            }
        }
    }
    {
        CCoinsView dummy;
        CCoinsViewCache view(&dummy);
        LockPoints lp;
        CCoinsViewMemPool viewMemPool(pcoinsTip.get(), pool);
        view.SetBackend(viewMemPool);
        
        for (const CTxIn& txin : tx.vin) {
            if (!pcoinsTip->HaveCoinInCache(txin.prevout)) {
                coins_to_uncache.push_back(txin.prevout);
            }
            if (!view.HaveCoin(txin.prevout)) {
                
                for (size_t out = 0; out < tx.vout.size(); out++) {
                    
                    if (pcoinsTip->HaveCoinInCache(COutPoint(hash, out))) {
                        return state.Invalid(false, REJECT_DUPLICATE, "txn-already-known");