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
```
CValidationState state;
    const CChainParams& chainparams = Params();
    if (!FlushStateToDisk(chainparams, state, FlushStateMode::ALWAYS)) {
        LogPrintf("%s: failed to flush state (%s)\n", __func__, FormatStateMessage(state));
    }
}
void PruneAndFlush() {
    CValidationState state;
    fCheckForPruning = true;
    const CChainParams& chainparams = Params();
    if (!FlushStateToDisk(chainparams, state, FlushStateMode::NONE)) {
        LogPrintf("%s: failed to flush state (%s)\n", __func__, FormatStateMessage(state));
    }
}
static void DoWarning(const std::string& strWarning)
{
    static bool fWarned = false;
    SetMiscWarning(strWarning);
    if (!fWarned) {
        AlertNotify(strWarning);
        fWarned = true;
    }
}
static void AppendWarning(std::string& res, const std::string& warn)