Returns the current header of the @row.
This can be used in a [callback@Gtk.ListBoxUpdateHeaderFunc] to see if there is a header set already, and if so to update the state of it.
the current header, or %NULL if none
See Implementation
Returns the current header of the @row.
This can be used in a [callback@Gtk.ListBoxUpdateHeaderFunc] to see if there is a header set already, and if so to update the state of it.