Don't add a label on RadioToolButton when set icon_widget - Fixes #4875
Don't add a label on RadioToolButton when set icon_widget - Fixes #4875

When we use set_icon_widget(), GtkToolButton set a private property
contents_invalid = TRUE [1], and gtk_tool_button_construct_content [2]
is called. Then if the label widget not exist, a GtkLabel is added.
This is a problem for us, by example in the Clipboard buttons in the frame.
By adding a empty Gtk.Box instead of a label, we avoid the label creation.

But as this is a internal implementation of Gtk, can change in the future,
in fact the issue is not visible with Gtk < 3.16

This patch is based in a pr sent by Sam Parkinson

[1] https://github.com/GNOME/gtk/blob/master/gtk/gtktoolbutton.c#L1415
[2] https://github.com/GNOME/gtk/blob/master/gtk/gtktoolbutton.c#L357

quozl/sugar-toolkit-gtk3,quozl/sugar-toolkit-gtk3,godiard/sugar-toolkit-gtk3,quozl/sugar-toolkit-gtk3,sugarlabs/sugar-toolkit-gtk3,i5o/sugar-toolkit-gtk3,Daksh/sugar-toolkit-gtk3,sugarlabs/sugar-toolkit-gtk3,i5o/sugar-toolkit-gtk3,Daksh/sugar-toolkit-gtk3,Daksh/sugar-toolkit-gtk3,godiard/sugar-toolkit-gtk3,i5o/sugar-toolkit-gtk3,godiard/sugar-toolkit-gtk3,sugarlabs/sugar-toolkit-gtk3,quozl/sugar-toolkit-gtk3,i5o/sugar-toolkit-gtk3