[fix] Use continue instead of return in manage_devices_group_templates

The loop in manage_devices_group_templates used `return` when a device
had no config, which aborted processing of all remaining devices in
the batch. Changed to `continue` so that devices without a config are
skipped individually while the rest of the batch is still processed.

Fixes silent configuration drift when batch-changing device groups
where some devices lack a config object.

Author: mn-ram

openwisp_controller/config/base/device.py

@@ -504,7 +504,7 @@ def manage_devices_group_templates(cls, device_ids, old_group_ids, group_id):
             config_created = hasattr(device, "config")
             if not config_created:
                 # device has no config (device group has no templates)
-                return
+                continue
             group_templates = Template.objects.none()
             if group_id:
                 group = DeviceGroup.objects.get(pk=group_id)