taker: Fix change validation logic

jmclient/jmclient/taker.py

@@ -485,12 +485,12 @@ class Taker(object):
         #we have tried to avoid this based on over-estimating the needed amount
         #in SendPayment.create_tx(), but it is still a possibility if one maker
         #uses a *lot* of inputs.
-        if self.my_change_addr and my_change_value <= 0:
+        if self.my_change_addr:
+            if my_change_value < 0:
                 raise ValueError("Calculated transaction fee of: " +
                     btc.amount_to_str(self.total_txfee) +
                     " is too large for our inputs; Please try again.")
-        elif self.my_change_addr and my_change_value <= jm_single(
+            if my_change_value <= jm_single().BITCOIN_DUST_THRESHOLD:
-        ).BITCOIN_DUST_THRESHOLD:
                 jlog.info("Dynamically calculated change lower than dust: " +
                     btc.amount_to_str(my_change_value) + "; dropping.")
                 self.my_change_addr = None