blockchain: sync: bug in get_and_write_currency_params
When the sync is started, in the case of a synchronization from zero, the currency and its parameters are not yet known. Currently, we get the parameters when receiving the 1st block to synchronize via a call to the function get_and_write_currency_params(). This function panics if we are not in the genesis block, we have to modify this behavior and go read the parameters in the database instead.