Issue 59744

1. Create an empty presentation, save it as "test.odp" and continue editing.
2. Insert a slide, layout "Title, Object".
3. Double click on "double click to add an object" and choose to create a new
   OOo 2.0 Text.
4. Write some text in the text object, then select Insert -> Fields -> Other...
   -> File name -> File name
5. A blank field is inserted.
6. Repeat steps 2-3-4 but this time insert an existing Writer document.
7. A blank field is shown where a "File Name" field appeared in the Writer
   document.

Expected result: 

If the "File name" refers to the object and is meaningless in this context, it
should be disabled.

If it has a meaning (e.g., is inherited from the parent "test.opd"), it should
be inserted properly.

[Reported by Flavio Aime during Italian QA tests]