Allow custom schedules to work again after #367

PR #367 and follow up edits were designed to give a sanity
check to users for fees, but require specifying a payment
amount, this could be generalised to custom schedules but
for now the simplest change is to remove this check for
schedules. Thanks to @roshii for flagging the error.

scripts/sendpayment.py

@@ -145,7 +145,9 @@ def main():
 
 
     # From the estimated tx fees, check if the expected amount is a
-    # significant value compared the the cj amount
+    # significant value compared the the cj amount; currently enabled
+    # only for single join (the predominant, non-advanced case)
+    if options.schedule == '':
         total_cj_amount = amount
         if total_cj_amount == 0:
             total_cj_amount = wallet_service.get_balance_by_mixdepth()[options.mixdepth]