Bugfix: The FSS Payload Read is not treating the Payload as raw when printing.

Bugfix: The FSS Payload Read is not treating the Payload as raw when printing.

Special handling is needed to process the `payload` section.
The content functions all need to have the `at` position to determine this.
Update the callbacks to allow for this.

The function `fss_read_print_content_empty()` is defined and used but it is used only for the `print_object_end_empty()` callback.
Add a `print_content_empty()` callback to provide this.

These changes allow for removing redundant functions.