Display anomalies in Black Box

[david-pfx]

@justkirb
Placing stones on the line of the beam allows the player to cheat and see the behavior of the beam.

Block the hidden path by marking blackboxes on the path, and then click on the desired side. There, the game will try to evaluate the beam of the side, but will be blocked by the marked blackboxes, causing red symbols to appear.

[david-pfx]

Sorry, yes sometimes I see it but no reliable repro case yet so I can't fix it.