Delete Button don´t work for "sonata_type_model_list"

Fix: getShortObjectDescriptionAction() now not return an 404, if no id is set.
Instead it the function returns the template with the "No selection" placeholder again.

The 404 wasnt correct here. 404 is now thrown, if an ID is given and the given ID isn´t available by getObject()

| Q             | A
| ------------- | ---
| Bug fix?      | [yes]
| New feature?  | [no]
| BC breaks?    | [no]
| Deprecations? | [no]
| Tests pass?   | [yes]
| Fixed tickets | [#1702]
| License       | MIT
| Doc PR        | []