improve ha client keepalive error handling

asyncua/client/ha/ha_client.py

@@ -450,6 +450,10 @@ class KeepAlive:
             f"Starting keepalive loop for {server_info.url}, checking every {self.timer}sec"
         )
         while self.is_running:
+            if client.uaclient.protocol is None:
+                server_info.status = ConnectionStates.NO_DATA
+                _logger.info("No active client")
+            else:
                 try:
                     status, slevel = await client.read_values([status_node, slevel_node])
                     if status != ua.ServerState.Running:
@@ -460,9 +464,12 @@ class KeepAlive:
                 except BadSessionNotActivated:
                     _logger.warning("Session is not yet activated.")
                     server_info.status = ConnectionStates.NO_DATA
-            except BadSessionClosed:
+                except BadSessionClosed :
                     _logger.warning("Session is closed.")
                     server_info.status = ConnectionStates.NO_DATA
+                except ConnectionError :
+                    _logger.warning("No connection.")
+                    server_info.status = ConnectionStates.NO_DATA
                 except asyncio.TimeoutError:
                     _logger.warning("Timeout when fetching state")
                     server_info.status = ConnectionStates.NO_DATA