List of steps to reproduce (step by step, including full links if applicable):

• Use Special:ApiSandbox to set any option to the default value (Special:ApiSandbox#action=options&format=json&change=watchdefault%3D1)
• Have a look at the logs, there is a delete statement for the user_properties table and the default option.
• Rerun the api
• There is still a delete, but there is never a row for this delete, it was deleted in the first step

What happens?:
If an app triggered many requests to the api's action=options to set options to the default value, it trigger delete statement and give pressure for the database, see T301433#7699716 for the problem/analyze

What should have happened instead?:
No delete is needed, there is no such a row
This would avoid the database (write) interaction for that unneeded web requests

Software version (if not a Wikimedia wiki), browser information, screenshots, other information, etc.: master