network - send_subscriptions: copy subscribed_addresses before iterating

see #4146
(this should at least avoid the RuntimeError)

lib/network.py

@@ -319,7 +319,7 @@ class Network(util.DaemonThread):
         self.queue_request('server.peers.subscribe', [])
         self.request_fee_estimates()
         self.queue_request('blockchain.relayfee', [])
-        for h in self.subscribed_addresses:
+        for h in list(self.subscribed_addresses):
             self.queue_request('blockchain.scripthash.subscribe', [h])
 
     def request_fee_estimates(self):