add a couple sanity checks to GetLastValidBlockHash
add a couple sanity checks to GetLastValidBlockHash

alejandromgk/Lunar,diggcoin/diggcoin,LIMXTEC/DMDv3,coinkeeper/2015-06-22_18-36_darkcoin,antcheck/antcoin,alejandromgk/Lunar,blood2/bloodcoin-0.9,Bloom-Project/Bloom,crowning-/dash,biblepay/biblepay,kbccoin/kbc,jmgilbert2/energi,Mrs-X/PIVX,ionomy/ion,biblepay/biblepay,48thct2jtnf/P,PIVX-Project/PIVX,ionomy/ion,thelazier/dash,CoinProjects/AmsterdamCoin-v4,diggcoin/diggcoin,ColossusCoinXT/ColossusCoinXT,blood2/bloodcoin-0.9,Darknet-Crypto/Darknet,cryptodev35/icash,mycointest/owncoin,BlockchainTechLLC/3dcoin,Petr-Economissa/gvidon,48thct2jtnf/P,terracoin/terracoin,coinkeeper/2015-06-22_18-36_darkcoin,terracoin/terracoin,lakepay/lake,keesdewit82/LasVegasCoin,puticcoin/putic,ahmedbodi/test2,RyanLucchese/energi,crowning-/dash,nmarley/dash,puticcoin/putic,ahmedbodi/test2,projectinterzone/ITZ,nightlydash/darkcoin,UdjinM6/dash,crowning2/dash,schinzelh/dash,knolza/gamblr,worldbit/worldbit,CoinProjects/AmsterdamCoin-v4,ediston/energi,ticclassic/ic,keesdewit82/LasVegasCoin,DMDcoin/Diamond,HeliumGas/helium,pelorusjack/BlockDX,Petr-Economissa/gvidon,Bloom-Project/Bloom,Bloom-Project/Bloom,willwray/dash,knolza/gamblr,slingcoin/sling-market,slingcoin/sling-market,DMDcoin/Diamond,ivansib/sib16,kbccoin/kbc,dev1972/Satellitecoin,schinzelh/dash,Petr-Economissa/gvidon,ivansib/sibcoin,HeliumGas/helium,mycointest/owncoin,mobicoins/mobicoin-core,rdqw/sscoin,biblepay/biblepay,diggcoin/diggcoin,ArgonToken/ArgonToken,dmrtsvetkov/flowercoin,crowning2/dash,benzmuircroft/REWIRE.io,cryptodev35/icash,Vsync-project/Vsync,ivansib/sib16,basicincome/unpcoin-core,benzmuircroft/REWIRE.io,grumpydevelop/singularity,rdqw/sscoin,inkvisit/sarmacoins,blood2/bloodcoin-0.9,jmgilbert2/energi,kbccoin/kbc,rsdevgun16e/energi,diggcoin/diggcoin,PIVX-Project/PIVX,puticcoin/putic,world-bank/unpay-core,mycointest/owncoin,Petr-Economissa/gvidon,kbccoin/kbc,cerebrus29301/crowncoin,ColossusCoinXT/ColossusCoinXT,projectinterzone/ITZ,RyanLucchese/energi,grumpydevelop/singularity,lakepay/lake,presstab/PIVX,ediston/energi,crowning2/dash,aspirecoin/aspire,worldbit/worldbit,ArgonToken/ArgonToken,crowning-/dash,48thct2jtnf/P,putinclassic/putic,ticclassic/ic,nightlydash/darkcoin,nightlydash/darkcoin,worldbit/worldbit,HeliumGas/helium,axelxod/braincoin,benzmuircroft/REWIRE.io,rdqw/sscoin,freelion93/mtucicoin,ivansib/sibcoin,ColossusCoinXT/ColossusCoinXT,dmrtsvetkov/flowercoin,putinclassic/putic,RyanLucchese/energi,presstab/PIVX,nmarley/dash,diggcoin/diggcoin,PandaPayProject/PandaPay,cryptodev35/icash,nmarley/dash,dev1972/Satellitecoin,diggcoin/diggcoin,Mrs-X/PIVX,ticclassic/ic,PandaPayProject/PandaPay,axelxod/braincoin,projectinterzone/ITZ,DMDcoin/Diamond,knolza/gamblr,cerebrus29301/crowncoin,Bloom-Project/Bloom,DMDcoin/Diamond,mycointest/owncoin,rdqw/sscoin,world-bank/unpay-core,aspirecoin/aspire,crowning-/dash,PandaPayProject/PandaPay,xuyangcn/opalcoin,inkvisit/sarmacoins,ivansib/sib16,blood2/bloodcoin-0.9,projectinterzone/ITZ,48thct2jtnf/P,nightlydash/darkcoin,thelazier/dash,thelazier/dash,freelion93/mtucicoin,keesdewit82/LasVegasCoin,ediston/energi,xuyangcn/opalcoin,biblepay/biblepay,freelion93/mtucicoin,freelion93/mtucicoin,mycointest/owncoin,pinkevich/dash,PIVX-Project/PIVX,UdjinM6/dash,biblepay/biblepay,knolza/gamblr,kbccoin/kbc,ArgonToken/ArgonToken,RyanLucchese/energi,CoinProjects/AmsterdamCoin-v4,dashpay/dash,npccoin/npccoin,ivansib/sibcoin,ahmedbodi/test2,rdqw/sscoin,schinzelh/dash,PIVX-Project/PIVX,slingcoin/sling-market,schinzelh/dash,aspirecoin/aspire,LIMXTEC/DMDv3,projectinterzone/ITZ,nmarley/dash,ivansib/sib16,antcheck/antcoin,DMDcoin/Diamond,alejandromgk/Lunar,slingcoin/sling-market,pinkevich/dash,Vsync-project/Vsync,dmrtsvetkov/flowercoin,DMDcoin/Diamond,presstab/PIVX,ahmedbodi/test2,knolza/gamblr,schinzelh/dash,pelorusjack/BlockDX,aspirecoin/aspire,dashpay/dash,HeliumGas/helium,coinkeeper/2015-06-22_18-36_darkcoin,keesdewit82/LasVegasCoin,mycointest/owncoin,npccoin/npccoin,antcheck/antcoin,slingcoin/sling-market,pelorusjack/BlockDX,pelorusjack/BlockDX,cryptodev35/icash,LIMXTEC/DMDv3,aspirecoin/aspire,RyanLucchese/energi,dev1972/Satellitecoin,rsdevgun16e/energi,pinkevich/dash,lakepay/lake,Mrs-X/Darknet,ivansib/sib16,RyanLucchese/energi,putinclassic/putic,willwray/dash,Bloom-Project/Bloom,inkvisit/sarmacoins,ColossusCoinXT/ColossusCoinXT,terracoin/terracoin,alejandromgk/Lunar,midnight-miner/LasVegasCoin,lakepay/lake,Darknet-Crypto/Darknet,ivansib/sib16,cryptodev35/icash,Mrs-X/Darknet,presstab/PIVX,worldbit/worldbit,slingcoin/sling-market,jmgilbert2/energi,BlockchainTechLLC/3dcoin,lakepay/lake,PIVX-Project/PIVX,worldbit/worldbit,midnight-miner/LasVegasCoin,midnight-miner/LasVegasCoin,world-bank/unpay-core,antcheck/antcoin,mobicoins/mobicoin-core,world-bank/unpay-core,putinclassic/putic,mobicoins/mobicoin-core,biblepay/biblepay,dashpay/dash,Darknet-Crypto/Darknet,Vsync-project/Vsync,HeliumGas/helium,CoinProjects/AmsterdamCoin-v4,antcheck/antcoin,pelorusjack/BlockDX,ionomy/ion,terracoin/terracoin,basicincome/unpcoin-core,Mrs-X/Darknet,Mrs-X/PIVX,midnight-miner/LasVegasCoin,schinzelh/dash,grumpydevelop/singularity,grumpydevelop/singularity,mobicoins/mobicoin-core,dmrtsvetkov/flowercoin,ivansib/sibcoin,biblepay/biblepay,crowning2/dash,PIVX-Project/PIVX,crowning-/dash,ColossusCoinXT/ColossusCoinXT,npccoin/npccoin,antcheck/antcoin,inkvisit/sarmacoins,mobicoins/mobicoin-core,nightlydash/darkcoin,PIVX-Project/PIVX,pinkevich/dash,rsdevgun16e/energi,dev1972/Satellitecoin,freelion93/mtucicoin,PandaPayProject/PandaPay,ColossusCoinXT/ColossusCoinXT,dmrtsvetkov/flowercoin,dashpay/dash,benzmuircroft/REWIRE.io,Mrs-X/Darknet,dmrtsvetkov/flowercoin,freelion93/mtucicoin,PIVX-Project/PIVX,PandaPayProject/PandaPay,BlockchainTechLLC/3dcoin,biblepay/biblepay,jmgilbert2/energi,Bloom-Project/Bloom,cerebrus29301/crowncoin,lakepay/lake,ahmedbodi/test2,basicincome/unpcoin-core,terracoin/terracoin,LIMXTEC/DMDv3,ArgonToken/ArgonToken,cerebrus29301/crowncoin,thelazier/dash,willwray/dash,dev1972/Satellitecoin,UdjinM6/dash,axelxod/braincoin,48thct2jtnf/P,LIMXTEC/DMDv3,Mrs-X/PIVX,Darknet-Crypto/Darknet,putinclassic/putic,Mrs-X/PIVX,ionomy/ion,LIMXTEC/DMDv3,rdqw/sscoin,ionomy/ion,Vsync-project/Vsync,benzmuircroft/REWIRE.io,Petr-Economissa/gvidon,crowning-/dash,axelxod/braincoin,Vsync-project/Vsync,pinkevich/dash,blood2/bloodcoin-0.9,alejandromgk/Lunar,PandaPayProject/PandaPay,knolza/gamblr,ionomy/ion,xuyangcn/opalcoin,nmarley/dash,worldbit/worldbit,rsdevgun16e/energi,Mrs-X/Darknet,world-bank/unpay-core,npccoin/npccoin,Darknet-Crypto/Darknet,nmarley/dash,keesdewit82/LasVegasCoin,Mrs-X/PIVX,coinkeeper/2015-06-22_18-36_darkcoin,benzmuircroft/REWIRE.io,basicincome/unpcoin-core,pinkevich/dash,UdjinM6/dash,rsdevgun16e/energi,inkvisit/sarmacoins,puticcoin/putic,xuyangcn/opalcoin,48thct2jtnf/P,alejandromgk/Lunar,ivansib/sibcoin,xuyangcn/opalcoin,ticclassic/ic,CoinProjects/AmsterdamCoin-v4,ticclassic/ic,thelazier/dash,puticcoin/putic,ticclassic/ic,ahmedbodi/test2,axelxod/braincoin,Petr-Economissa/gvidon,nmarley/dash,ArgonToken/ArgonToken,willwray/dash,dev1972/Satellitecoin,presstab/PIVX,BlockchainTechLLC/3dcoin,PIVX-Project/PIVX,crowning2/dash,Vsync-project/Vsync,BlockchainTechLLC/3dcoin,keesdewit82/LasVegasCoin,willwray/dash,willwray/dash,inkvisit/sarmacoins,cerebrus29301/crowncoin,grumpydevelop/singularity,ArgonToken/ArgonToken,ediston/energi,grumpydevelop/singularity,ediston/energi,npccoin/npccoin,terracoin/terracoin,ediston/energi,dashpay/dash,aspirecoin/aspire,cerebrus29301/crowncoin,basicincome/unpcoin-core,puticcoin/putic,midnight-miner/LasVegasCoin,jmgilbert2/energi,HeliumGas/helium,ivansib/sibcoin,jmgilbert2/energi,midnight-miner/LasVegasCoin,Darknet-Crypto/Darknet,xuyangcn/opalcoin,presstab/PIVX,axelxod/braincoin,npccoin/npccoin,coinkeeper/2015-06-22_18-36_darkcoin,rsdevgun16e/energi,UdjinM6/dash,putinclassic/putic,BlockchainTechLLC/3dcoin,CoinProjects/AmsterdamCoin-v4,pelorusjack/BlockDX,Mrs-X/Darknet