Saving a hot folder that contains a job chain without nodes leads into endless reload questions and a stacktrace is shown

Description
When a new job chain will be created and no nodes are defined, it is not possible to save the hot folder.

• A stacktrace is shown. That states a problem while validating against the xsd schema.
• A confirm is shown, whether the file should be saved
• In case of answer no, an error is show "Could not rename.."
• Clicking ok again shows a stacktrace

*Desired behaviour"
When saving a job chain that does not contain a node, a warning should be shown. It should be possible to save the file after confirmation.

To reproduce
Create a new job chain without nodes and click the save button.