Better fix for issue1550

Reuse image of the button instead of creating a new one

tryton/gui/window/view_form/view/form_gtk/many2one.py

@@ -285,17 +285,15 @@ class Many2One(WidgetInterface):
             self.wid_text.set_text('')
             self.changed = True
             return False
+        img = self.but_open.get_image()
         current_stock = img.get_stock()[0]
         res = field.get_client(record)
         self.wid_text.set_text((res and str(res)) or '')
-        img = gtk.Image()
         if res and current_stock != 'tryton-open':
             img.set_from_stock('tryton-open', gtk.ICON_SIZE_SMALL_TOOLBAR)
-            self.but_open.set_image(img)
             self.tooltips.set_tip(self.but_open, _('Open a record'))
         elif not res and current_stock != 'tryton-find':
             img.set_from_stock('tryton-find', gtk.ICON_SIZE_SMALL_TOOLBAR)
-            self.but_open.set_image(img)
             self.tooltips.set_tip(self.but_open, _('Search a record'))
         self.changed = True