RPC: Fix a crash when calling 'getwitnessinfo' on first few blocks in chain
RPC: Fix a crash when calling 'getwitnessinfo' on first few blocks in chain

nlgcoin/guldencoin-official,nlgcoin/guldencoin-official,nlgcoin/guldencoin-official,nlgcoin/guldencoin-official,nlgcoin/guldencoin-official,nlgcoin/guldencoin-official