dwb_critics flaky test - lineCost coordinates must be within costmap (#4889)

(#4884)

There is no protection/checks in the pathway from lineCost to
costmap_2d::getIndex(mx, my) for grid coordinates that exceed
the of bounds of the allocated costmap. (presumably for speed)

This test was triggering an off by one error attempting to
read the the 2500 byte costmap at byte 2503

costmap size 50x50.

getIndex(3, 50)
= my * size_x_ + mx;
= 50 * 50 + 3;
= 2503

Signed-off-by: Mike Wake <macwake@gmail.com>

Author: ewak

nav2_dwb_controller/dwb_critics/test/obstacle_footprint_test.cpp

@@ -248,7 +248,9 @@ TEST(ObstacleFootprint, LineCost)
   costmap_ros->getCostmap()->setCost(4, 3, 100);
   costmap_ros->getCostmap()->setCost(4, 4, 100);
 
-  ASSERT_EQ(critic->lineCost(3, 3, 0, 50), 50);   // all 50
+  auto max_y_in_grid_coordinates = costmap_ros->getCostmap()->getSizeInCellsY() - 1;
+  ASSERT_EQ(max_y_in_grid_coordinates, 49);
+  ASSERT_EQ(critic->lineCost(3, 3, 0, max_y_in_grid_coordinates), 50);   // all 50
   ASSERT_EQ(critic->lineCost(4, 4, 0, 10), 100);  // all 100
   ASSERT_EQ(critic->lineCost(0, 50, 3, 3), 100);  // pass 50 and 100
 }