Do not close non existing clients in modbus (#49489)

* Only close if _client is present.

* Remove del.

homeassistant/components/modbus/modbus.py

@@ -209,11 +209,11 @@ class ModbusHub:
         """Disconnect client."""
         with self._lock:
             try:
+                if self._client:
                     self._client.close()
-                del self._client
                     self._client = None
             except ModbusException as exception_error:
-                self._log_error(exception_error, error_state=False)
+                self._log_error(exception_error)
                 return
 
     def connect(self):