Merge pull request #4 from isocolsky/fix/build-tx

assert inputs & outputs are consistent

lib/model/txproposal.js

@@ -185,6 +185,7 @@ TxProposal.prototype._buildTx = function() {
   var totalInputs = _.sum(t.inputs, 'output.satoshis');
   var totalOutputs = _.sum(t.outputs, 'satoshis');
 
+  $.checkState(totalInputs > 0 && totalOutputs > 0 && totalInputs >= totalOutputs);
   $.checkState(totalInputs - totalOutputs <= Defaults.MAX_TX_FEE);
 
   return t;