always assume change output exists when estimating fee

src/wallet.js

@@ -191,14 +191,12 @@ var Wallet = function (seed, options) {
           totalInValue += output.value
           if(totalInValue < value) continue;
 
-          var fee = fixedFee || tx.estimateFee()
+          var fee = fixedFee || estimateFeePadChangeOutput(tx)
           if(totalInValue < value + fee) continue;
 
           var change = totalInValue - value - fee
-          var changeAddress = getChangeAddress()
           if(change > 0) {
-            tx.addOutput(changeAddress, change)
-            // TODO: recalculate fee
+            tx.addOutput(getChangeAddress(), change)
           }
           break;
         }
@@ -207,6 +205,12 @@ var Wallet = function (seed, options) {
         return tx
     }
 
+    function estimateFeePadChangeOutput(tx){
+        var tmpTx = tx.clone()
+        tmpTx.addOutput(getChangeAddress(), 0)
+        return tmpTx.estimateFee()
+    }
+
     function getChangeAddress() {
       if(me.changeAddresses.length === 0) me.generateChangeAddress()
       return me.changeAddresses[me.changeAddresses.length - 1]