Test if exposed before using computed values in motion

In some cases, motion event is triggered before expose.
So motion method should take care of such case.

issue3755
review4301002

tryton/gui/window/view_form/view/graph_gtk/bar.py

@@ -65,6 +65,9 @@ class Bar(Graph):
     def motion(self, widget, event):
         super(Bar, self).motion(widget, event)
 
+        if not getattr(self, 'area', None):
+            return
+
         def intersect(bar, event):
             x = self.area.w * bar.x + self.area.x
             y = self.area.h * bar.y + self.area.y

tryton/gui/window/view_form/view/graph_gtk/line.py

@@ -154,6 +154,9 @@ class Line(Graph):
         cr.restore()
 
     def motion(self, widget, event):
+        if not getattr(self, 'area', None):
+            return
+
         nearest = None
         for point in self.points:
             x = point.x * self.area.w + self.area.x

tryton/gui/window/view_form/view/graph_gtk/pie.py

@@ -108,6 +108,9 @@ class Pie(Graph):
     def motion(self, widget, event):
         super(Pie, self).motion(widget, event)
 
+        if not getattr(self, 'area', None):
+            return
+
         d = (event.x - self.centerx) ** 2 + (event.y - self.centery) ** 2
         if d > self.radius ** 2:
             self.popup.hide()