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
```
invalid_walk_tip = invalid_walk_tip->pprev;
    }
    
    pindex->nStatus |= BLOCK_FAILED_VALID;
    setDirtyBlockIndex.insert(pindex);
    setBlockIndexCandidates.erase(pindex);
    m_failed_blocks.insert(pindex);
    
    
    UpdateMempoolForReorg(disconnectpool, true);
    
    
    BlockMap::iterator it = mapBlockIndex.begin();
    while (it != mapBlockIndex.end()) {
        if (it->second->IsValid(BLOCK_VALID_TRANSACTIONS) && it->second->HaveTxsDownloaded() && !setBlockIndexCandidates.value_comp()(it->second, chainActive.Tip())) {
            setBlockIndexCandidates.insert(it->second);
        }
        it++;
    }
    InvalidChainFound(pindex);
    
    if (pindex_was_in_chain) {
        uiInterface.NotifyBlockTip(IsInitialBlockDownload(), pindex->pprev);
    }
    return true;
}
bool InvalidateBlock(CValidationState& state, const CChainParams& chainparams, CBlockIndex *pindex) {
    return g_chainstate.InvalidateBlock(state, chainparams, pindex);
}
void CChainState::ResetBlockFailureFlags(CBlockIndex *pindex) {