Fix height assertion in Blockchain::handle_alternative_block()
Fix height assertion in Blockchain::handle_alternative_block()

It expects the total number of blocks of main chain, not last block id
(off-by-one error).

This again behaves like the same height assertion done in original
implementation in blockchain_storage::handle_alternative_block().

This allows a reorganization to proceed after an alternative block has
been added.

ranok/bitmonero,eiabea/bitmonero,ranok/bitmonero,ranok/bitmonero,ranok/bitmonero,eiabea/bitmonero,eiabea/bitmonero,eiabea/bitmonero,eiabea/bitmonero,ranok/bitmonero,ranok/bitmonero,eiabea/bitmonero