UnspentOutput: Fix issue when 0 being feed as amount

lib/transaction/unspentoutput.js

@@ -41,9 +41,9 @@ function UnspentOutput(data) {
   if (!_.isNumber(outputIndex)) {
     throw new Error('Invalid outputIndex, received ' + outputIndex);
   }
-  $.checkArgument(data.scriptPubKey || data.script, 'Must provide the scriptPubKey for that output!');
+  $.checkArgument(!_.isUndefined(data.scriptPubKey || data.script), 'Must provide the scriptPubKey for that output!');
   var script = new Script(data.scriptPubKey || data.script);
-  $.checkArgument(data.amount || data.satoshis, 'Must provide the scriptPubKey for that output!');
+  $.checkArgument(!_.isUndefined(data.amount || data.satoshis), 'Must provide an amount for the output');
   var amount = data.amount ? new Unit.fromBTC(data.amount).toSatoshis() : data.satoshis;
   $.checkArgument(_.isNumber(amount), 'Amount must be a number');
   JSUtil.defineImmutable(this, {