If the frame’s label widget is a #GtkLabel, returns the
text in the label widget. (The frame will have a #GtkLabel
for the label widget if a non-%NULL argument was passed
to gtk_frame_new().)
the text in the label, or %NULL if there
was no label widget or the lable widget was not
a #GtkLabel. This string is owned by GTK+ and
must not be modified or freed.
If the frame’s label widget is a #GtkLabel, returns the text in the label widget. (The frame will have a #GtkLabel for the label widget if a non-%NULL argument was passed to gtk_frame_new().)