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
```
{
    CDiskBlockPos hpos = pos;
    hpos.nPos -= 8; 
    CAutoFile filein(OpenBlockFile(hpos, true), SER_DISK, CLIENT_VERSION);
    if (filein.IsNull()) {
        return error("%s: OpenBlockFile failed for %s", __func__, pos.ToString());
    }
    try {
        CMessageHeader::MessageStartChars blk_start;
        unsigned int blk_size;
        filein >> blk_start >> blk_size;
        if (memcmp(blk_start, message_start, CMessageHeader::MESSAGE_START_SIZE)) {
            return error("%s: Block magic mismatch for %s: %s versus expected %s", __func__, pos.ToString(),
                    HexStr(blk_start, blk_start + CMessageHeader::MESSAGE_START_SIZE),
                    HexStr(message_start, message_start + CMessageHeader::MESSAGE_START_SIZE));
        }
        if (blk_size > MAX_SIZE) {
            return error("%s: Block data is larger than maximum deserialization size for %s: %s versus %s", __func__, pos.ToString(),
                    blk_size, MAX_SIZE);
        }
        block.resize(blk_size); 
        filein.read((char*)block.data(), blk_size);
    } catch(const std::exception& e) {
        return error("%s: Read from block file failed: %s for %s", __func__, e.what(), pos.ToString());
    }
    return true;
}
bool ReadRawBlockFromDisk(std::vector<uint8_t>& block, const CBlockIndex* pindex, const CMessageHeader::MessageStartChars& message_start)