Fix debris after click-click explosion near board edge

Fix debris after click-click explosion near board edge

The redrawn grid was not exposed for board edges a knight's jump
away from an explosion square after a click-click capture in variant
atomic. This was due to the smartness in preventing overlapping
exposures of neighboring square, deferring the task to expose the grid
to squares that were beyond the edge. Now all squares in the explosion
range are exposed including grid.