invalidateblock goes back one block at a time, and doesn't reorg properly

[roylee17]

For example,

100 -> 101 -> 102 -> 103  (main chain)
     \ 101a (side chain)

1. invalidate one block at a time from the tip works.

$ getbestblock
{
  hash: HASH_OF_103
  height: 103
}

$ invalidateblock HASH_OF_103
$ invalidateblock HASH_OF_102

$ getbestblock
{
  hash: HASH_OF_101
  height: 101
}

2. However, even if we invalidate block 101, the main chain doesn't reorg properly to block 101a

$ invalidateblock HASH_OF_101 
$ getbestblock
{
  hash: HASH_OF_101a
  height: 101a
}
$ getblock HASH_OF_101a
block HASH_OF_101a is not in the main chain

3. invalidate more than one block at a time cause lbcd goes rogue. Starting to exhaust CPU and memory.

$ getbestblock
{
  hash: HASH_OF_103
  height: 103
}

$ invalidateblock HASH_OF_101
(lbcd goes rogue...)

[roylee17]

lbryio/lbry-sdk#3520