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
```
{
    LOCK(cs_main);
    CCoinsViewCache cache(view);
    std::vector<uint256> hashHeads = view->GetHeadBlocks();
    if (hashHeads.empty()) return true; 
    if (hashHeads.size() != 2) return error("ReplayBlocks(): unknown inconsistent state");
    uiInterface.ShowProgress(_("Replaying blocks..."), 0, false);
    LogPrintf("Replaying blocks\n");
    const CBlockIndex* pindexOld = nullptr;  
    const CBlockIndex* pindexNew;            
    const CBlockIndex* pindexFork = nullptr; 
    if (mapBlockIndex.count(hashHeads[0]) == 0) {
        return error("ReplayBlocks(): reorganization to unknown block requested");
    }
    pindexNew = mapBlockIndex[hashHeads[0]];
    if (!hashHeads[1].IsNull()) { 
        if (mapBlockIndex.count(hashHeads[1]) == 0) {
            return error("ReplayBlocks(): reorganization from unknown block requested");
        }
        pindexOld = mapBlockIndex[hashHeads[1]];
        pindexFork = LastCommonAncestor(pindexOld, pindexNew);
        assert(pindexFork != nullptr);
    }
    
    while (pindexOld != pindexFork) {
        if (pindexOld->nHeight > 0) {