Depth min/max should be one pass

[MatejSakmary]

Atomic add to a global variable for each wg that already finished - I can use this to kill the amount of wgs that are not needed for the second pass.

For example:
If 4 wgs in first pass map to 1wg in second pass you just wait till the atomic add returns multiple of three. Then you know you are the one wg the previous 4 map to and you can also be sure they already finished their work so you can read the results.