Block button handler instead of deactivate button

By deactivating the button, the button lost the focus which makes NoModal
selects the wrong sensitive widget and thus the wizard behaves like if it was
launched from the menu instead of from a tab.

issue3353
review1083003

tryton/gui/window/view_form/view/form.py

@@ -178,8 +178,8 @@ class ViewForm(ParserView):
             self.screen.display(set_cursor=True)
             return
         else:
-            widget.set_sensitive(False)
+            widget.handler_block_by_func(self.button_clicked)
             try:
                 self.screen.button(widget.attrs)
             finally:
-                widget.set_sensitive(True)
+                widget.handler_unblock_by_func(self.button_clicked)