[Freeciv-Dev] (PR#4188) get_defender() given illegal combat options

["Per I. Mathisen" <per@xxxxxxxxxxx>]

ai/aiunit.c, find_something_to_kill():

     if (!(aunit == get_defender(punit, aunit->x, aunit->y))) {
        /* It's not the main defender */
        continue;
      }

This can attempt to make a defender in illegal conditions, which in turn
leads to an assert failure in get_defender().

One solution is to remove the error checking from get_defender(). I don't
find that a good idea.

Another is to make a wrapping function for get_defender() for the AI for
whenever we use it virtually.

But best of all, I think we can just add a call to
can_unit_attack_unit_at_tile() to the above mess.

Greg? You touched this code last.

  - Per