fix [#34113] operator_menu_enum() - Tooltip not showing descriptions

second fix from this report which makes the menu show tips even when 'bl_property' isn't set.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54314 954f8c5b-7b00-dc11-b283-0030488c597c