Auto merge of #1547 - daira:1378-witness-cache-assertion-failure.1, r=bitcartel
Auto merge of #1547 - daira:1378-witness-cache-assertion-failure.1, r=bitcartel

Add more precise assertions in IncrementNoteWitnesses

Part of #1378

bitcoinsSG/zcash,bitcoinsSG/zcash,bitcoinsSG/zcash,bitcoinsSG/zcash,bitcoinsSG/zcash,bitcoinsSG/zcash