Fix compiler warning about cases not handled in switch (#8262)

Source/missiles.cpp

@@ -760,7 +760,7 @@ bool TryGrowWall(int id, MissileID type, Point position, Direction growDirection
 	case Direction::South:
 	case Direction::West:
 	case Direction::North:
-	case Direction::East:
+	case Direction::East: {
 		Point gapPos = position + Displacement(Right(growDirection)) - Displacement(growDirection);
 		if (CanPlaceWall(gapPos)) {
 			Missile *missile = PlaceWall(id, type, gapPos, direction, spellLevel, damage);
@@ -775,6 +775,9 @@ bool TryGrowWall(int id, MissileID type, Point position, Direction growDirection
 		}
 		break;
 	}
+	default:
+		break;
+	}
 
 	if (!CanPlaceWall(position))
 		return false;