txdb: add assert.

lib/wallet/txdb.js

@@ -1681,6 +1681,7 @@ TXDB.prototype.fillHistory = function fillHistory(tx) {
       var index = layout.dd(key)[1];
       var coin = Coin.fromRaw(value);
       var input = tx.inputs[index];
+      assert(input);
       coin.hash = input.prevout.hash;
       coin.index = input.prevout.index;
       input.coin = coin;