Plane: fixed negative loiter radius values

ArduPlane/navigation.cpp

@@ -139,7 +139,7 @@ void Plane::update_loiter(uint16_t radius)
 {
     if (radius <= 1) {
         // if radius is <=1 then use the general loiter radius. if it's small, use default
-        radius = (abs(g.loiter_radius <= 1)) ? LOITER_RADIUS_DEFAULT : abs(g.loiter_radius);
+        radius = (abs(g.loiter_radius) <= 1) ? LOITER_RADIUS_DEFAULT : abs(g.loiter_radius);
         loiter.direction = (g.loiter_radius < 0) ? -1 : 1;
     }