added double-check for 202612 block id
added double-check for 202612 block id

if a new block has the same block id as 202612 but the wrong blobdata,
this will tell the caller that the block id is actually null_hash rather
than the 202612 block id.

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