fix subscription cancel webhook

rowers/braintreestuff.py

@@ -68,6 +68,8 @@ def process_webhook(notification):
         subscription = notification.subscription
         rs = Rower.objects.filter(subscription_id=subscription.id)
         if rs.count() == 0:
+            with open('braintreewebhooks.log','a') as f:
+                f.write('Could not find rowers with subscription ID '+subscription.id+'\n')
             return 0
         r = rs[0]
         result,mesg,errormsg = cancel_subscription(r,subscription.id)