RadioToolButton: make sure _hide_tooltip_on_click is initialized in time

If we pass the active property to the constructor do_clicked seem
to get called. Before chaining up to the Gtk.RadioToolButton
constructor we need to initialize the variable.

This is a followup of 5a1b380dd6

Signed-off-by: Simon Schampijer <simon@laptop.org>
Tested-by: Gonzalo Odiard <gonzalo@laptop.org>
Acked-by: Manuel Quiñones <manuq@laptop.org>

src/sugar3/graphics/radiotoolbutton.py

@@ -37,12 +37,13 @@ class RadioToolButton(Gtk.RadioToolButton):
         self._accelerator = None
         self._tooltip = None
         self._xo_color = None
+        self._hide_tooltip_on_click = True
+
         self._palette_invoker = ToolInvoker()
 
         GObject.GObject.__init__(self, **kwargs)
 
         self._palette_invoker.attach_tool(self)
-        self._hide_tooltip_on_click = True
 
         if icon_name:
             self.set_icon_name(icon_name)