Allow stop() even if start() hasnt been called yet, for more graceful degradation.

RCUSCC/RCUSCC/opcua_connection.py

@@ -74,6 +74,10 @@ class OPCUAConnection(Thread):
           Stop connecting & disconnect. Can take a few seconds for the timeouts to hit.
         """
 
+        if not self.ident:
+            # have not yet been started, so nothing to do
+            return
+
         self.stopping = True
         self.join()