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
```
{
    AssertLockHeld(cs_main);
    if (chainActive.Tip() && chainActive.Tip()->GetBlockHash() == pcoinsTip->GetBestBlock()) return true;
    if (pcoinsTip->GetBestBlock().IsNull() && mapBlockIndex.size() == 1) {
        
        
        LogPrintf("%s: Connecting genesis block...\n", __func__);
        CValidationState state;
        if (!ActivateBestChain(state, chainparams)) {
            LogPrintf("%s: failed to activate chain (%s)\n", __func__, FormatStateMessage(state));
            return false;
        }
    }
    
    CBlockIndex* pindex = LookupBlockIndex(pcoinsTip->GetBestBlock());
    if (!pindex) {
        return false;
    }
    chainActive.SetTip(pindex);
    g_chainstate.PruneBlockIndexCandidates();
    LogPrintf("Loaded best chain: hashBestChain=%s height=%d date=%s progress=%f\n",
        chainActive.Tip()->GetBlockHash().ToString(), chainActive.Height(),
        FormatISO8601DateTime(chainActive.Tip()->GetBlockTime()),
        GuessVerificationProgress(chainparams.TxData(), chainActive.Tip()));
    return true;
}
CVerifyDB::CVerifyDB()