Block count is literally a block counter, while block height is the height
written in the block. For block zero the height is zero while we have one block
in the chain and therefore the count is one. Persistent store operates with
heights, therefore comparison should be adjusted by one.

Signed-off-by: Roman Khimov <roman@nspcc.ru>

We can have a set of RPC nodes configured and we will switch them in runtime,
but if the first node is outdated then the IR node will _always_ fail to
start until RPC node catches up. We can have a better behaviour with node
switching to other RPCs in this phase.

Can't be done this easily for the sidechain since in most cases we have an
internal node and it needs to go through the chain completely.

Refs. #2426.

Signed-off-by: Roman Khimov <roman@nspcc.ru>