walletdb: Ensure that having no database handle is a failure
walletdb: Ensure that having no database handle is a failure

Previously having no database handle could still be considered a success
when BerkeleyDatabase and BerkeleyBatch were used for dummy database
things. With dedicated DummyDatabase and DummyBatch classes now, these
should fail.

ElementsProject/elements,fujicoin/fujicoin,lateminer/bitcoin,MeshCollider/bitcoin,ajtowns/bitcoin,mruddy/bitcoin,pstratem/bitcoin,prusnak/bitcoin,jamesob/bitcoin,anditto/bitcoin,rnicoll/dogecoin,andreaskern/bitcoin,MeshCollider/bitcoin,Sjors/bitcoin,n1bor/bitcoin,jnewbery/bitcoin,alecalve/bitcoin,EthanHeilman/bitcoin,GroestlCoin/GroestlCoin,qtumproject/qtum,ajtowns/bitcoin,practicalswift/bitcoin,litecoin-project/litecoin,dscotese/bitcoin,qtumproject/qtum,qtumproject/qtum,domob1812/namecore,ajtowns/bitcoin,dscotese/bitcoin,MeshCollider/bitcoin,particl/particl-core,sipsorcery/bitcoin,instagibbs/bitcoin,EthanHeilman/bitcoin,anditto/bitcoin,AkioNak/bitcoin,practicalswift/bitcoin,ajtowns/bitcoin,Xekyo/bitcoin,mruddy/bitcoin,domob1812/bitcoin,n1bor/bitcoin,AkioNak/bitcoin,rnicoll/bitcoin,instagibbs/bitcoin,pataquets/namecoin-core,rnicoll/bitcoin,jambolo/bitcoin,domob1812/namecore,apoelstra/bitcoin,tecnovert/particl-core,Xekyo/bitcoin,sipsorcery/bitcoin,domob1812/namecore,pstratem/bitcoin,namecoin/namecoin-core,Xekyo/bitcoin,yenliangl/bitcoin,jamesob/bitcoin,fujicoin/fujicoin,yenliangl/bitcoin,andreaskern/bitcoin,pstratem/bitcoin,achow101/bitcoin,mm-s/bitcoin,jnewbery/bitcoin,MarcoFalke/bitcoin,namecoin/namecoin-core,lateminer/bitcoin,domob1812/namecore,mm-s/bitcoin,JeremyRubin/bitcoin,AkioNak/bitcoin,MarcoFalke/bitcoin,domob1812/bitcoin,EthanHeilman/bitcoin,ElementsProject/elements,domob1812/bitcoin,fanquake/bitcoin,GroestlCoin/GroestlCoin,jambolo/bitcoin,particl/particl-core,apoelstra/bitcoin,anditto/bitcoin,dscotese/bitcoin,sstone/bitcoin,pataquets/namecoin-core,prusnak/bitcoin,qtumproject/qtum,lateminer/bitcoin,mruddy/bitcoin,bitcoinknots/bitcoin,anditto/bitcoin,kallewoof/bitcoin,fujicoin/fujicoin,prusnak/bitcoin,litecoin-project/litecoin,GroestlCoin/bitcoin,MeshCollider/bitcoin,anditto/bitcoin,fanquake/bitcoin,jambolo/bitcoin,alecalve/bitcoin,bitcoin/bitcoin,bitcoinknots/bitcoin,pataquets/namecoin-core,MeshCollider/bitcoin,sstone/bitcoin,prusnak/bitcoin,sstone/bitcoin,domob1812/namecore,apoelstra/bitcoin,jlopp/statoshi,sstone/bitcoin,Xekyo/bitcoin,ajtowns/bitcoin,cdecker/bitcoin,particl/particl-core,cdecker/bitcoin,JeremyRubin/bitcoin,ElementsProject/elements,namecoin/namecoin-core,bitcoinsSG/bitcoin,andreaskern/bitcoin,rnicoll/bitcoin,MarcoFalke/bitcoin,cdecker/bitcoin,namecoin/namecore,particl/particl-core,mm-s/bitcoin,jambolo/bitcoin,fanquake/bitcoin,sipsorcery/bitcoin,rnicoll/bitcoin,lateminer/bitcoin,mruddy/bitcoin,mm-s/bitcoin,namecoin/namecore,particl/particl-core,jonasschnelli/bitcoin,achow101/bitcoin,Xekyo/bitcoin,Sjors/bitcoin,bitcoinsSG/bitcoin,Sjors/bitcoin,apoelstra/bitcoin,kallewoof/bitcoin,namecoin/namecoin-core,ElementsProject/elements,domob1812/bitcoin,litecoin-project/litecoin,alecalve/bitcoin,cdecker/bitcoin,AkioNak/bitcoin,tecnovert/particl-core,rnicoll/dogecoin,ElementsProject/elements,JeremyRubin/bitcoin,yenliangl/bitcoin,sipsorcery/bitcoin,rnicoll/bitcoin,domob1812/namecore,jambolo/bitcoin,AkioNak/bitcoin,instagibbs/bitcoin,GroestlCoin/GroestlCoin,mruddy/bitcoin,pataquets/namecoin-core,bitcoinsSG/bitcoin,pstratem/bitcoin,kallewoof/bitcoin,GroestlCoin/bitcoin,qtumproject/qtum,jnewbery/bitcoin,Sjors/bitcoin,EthanHeilman/bitcoin,fujicoin/fujicoin,JeremyRubin/bitcoin,qtumproject/qtum,instagibbs/bitcoin,pataquets/namecoin-core,litecoin-project/litecoin,mruddy/bitcoin,fanquake/bitcoin,apoelstra/bitcoin,fanquake/bitcoin,domob1812/bitcoin,namecoin/namecore,dscotese/bitcoin,AkioNak/bitcoin,jlopp/statoshi,jlopp/statoshi,jonasschnelli/bitcoin,sipsorcery/bitcoin,JeremyRubin/bitcoin,jamesob/bitcoin,rnicoll/dogecoin,bitcoin/bitcoin,jonasschnelli/bitcoin,GroestlCoin/bitcoin,jlopp/statoshi,mm-s/bitcoin,prusnak/bitcoin,sipsorcery/bitcoin,namecoin/namecoin-core,cdecker/bitcoin,achow101/bitcoin,bitcoinknots/bitcoin,MarcoFalke/bitcoin,domob1812/bitcoin,MarcoFalke/bitcoin,litecoin-project/litecoin,bitcoinknots/bitcoin,MarcoFalke/bitcoin,qtumproject/qtum,yenliangl/bitcoin,tecnovert/particl-core,sstone/bitcoin,GroestlCoin/bitcoin,pstratem/bitcoin,cdecker/bitcoin,GroestlCoin/GroestlCoin,namecoin/namecore,tecnovert/particl-core,jonasschnelli/bitcoin,bitcoinsSG/bitcoin,litecoin-project/litecoin,yenliangl/bitcoin,n1bor/bitcoin,alecalve/bitcoin,bitcoin/bitcoin,n1bor/bitcoin,bitcoinsSG/bitcoin,bitcoin/bitcoin,instagibbs/bitcoin,EthanHeilman/bitcoin,lateminer/bitcoin,practicalswift/bitcoin,jambolo/bitcoin,jlopp/statoshi,jnewbery/bitcoin,achow101/bitcoin,namecoin/namecore,kallewoof/bitcoin,jonasschnelli/bitcoin,bitcoin/bitcoin,achow101/bitcoin,instagibbs/bitcoin,bitcoinsSG/bitcoin,lateminer/bitcoin,prusnak/bitcoin,dscotese/bitcoin,achow101/bitcoin,dscotese/bitcoin,ajtowns/bitcoin,practicalswift/bitcoin,pataquets/namecoin-core,particl/particl-core,bitcoin/bitcoin,n1bor/bitcoin,kallewoof/bitcoin,apoelstra/bitcoin,andreaskern/bitcoin,MeshCollider/bitcoin,tecnovert/particl-core,sstone/bitcoin,JeremyRubin/bitcoin,andreaskern/bitcoin,fujicoin/fujicoin,fanquake/bitcoin,Xekyo/bitcoin,alecalve/bitcoin,kallewoof/bitcoin,GroestlCoin/bitcoin,andreaskern/bitcoin,n1bor/bitcoin,bitcoinknots/bitcoin,GroestlCoin/GroestlCoin,jamesob/bitcoin,practicalswift/bitcoin,rnicoll/dogecoin,yenliangl/bitcoin,rnicoll/bitcoin,jlopp/statoshi,tecnovert/particl-core,Sjors/bitcoin,fujicoin/fujicoin,ElementsProject/elements,jnewbery/bitcoin,EthanHeilman/bitcoin,jamesob/bitcoin,mm-s/bitcoin,alecalve/bitcoin,GroestlCoin/GroestlCoin,jamesob/bitcoin,practicalswift/bitcoin,namecoin/namecoin-core,namecoin/namecore,GroestlCoin/bitcoin,rnicoll/dogecoin,anditto/bitcoin,pstratem/bitcoin