Goto path waypoint marker not shown if not at turn boundary
Noticed while looking at bug #856798:
If you set a waypoint on the goto path of a fast unit (like Horsemen on Grassland), then the path.waypoint 'flag' marker only shows up if some other symbol is already displayed: if the cursor is still at the waypoint, or if the waypoint is on a turn boundary.
The waypoint otherwise functions correctly.
Fortunately the cause and fix are trivial.