fix: set client-side SecureConnection state to 'open' on OpenSecureChannelResponse

See #745

Author: brubbel

opcua/common/connection.py

@@ -148,6 +148,7 @@ def set_channel(self, channel):
         Called on client side when getting secure channel data from server
         """
         self.channel = channel
+        self._open = True
 
     def open(self, params, server):
         """