leveldb: Fix dbIter that not being executing user-defined releaser
leveldb: Fix dbIter that not being executing user-defined releaser

zzl0/goleveldb,btcsuite/goleveldb,FactomProject/goleveldb,hustbill/goleveldb,conseweb/goleveldb,trigrass2/goleveldb,syndtr/goleveldb,rentongzhang/goleveldb,chai2010/goleveldb,ngaut/goleveldb,no2key/goleveldb