Explicitly state our assumptions about LookupBlockIndex(...) return values

[practicalswift]

Explicitly state our assumptions about LookupBlockIndex(...) return values.

[promag]

Concept ACK, but current change makes the code kind of ugly.

I wonder if adding the following is preferable:

// The caller knows the block index exists for the given block hash
inline CBlockIndex* GetBlockIndex(const uint256& hash)
{
    CBlockIndex* index = LookupBlockIndex(hash);
    assert(index);
    return index;
}