[Bug] Segmentation Id with 2 ** 32 - 1 is rendered completely white

[MichaelBuessemeyer]

Context

When having a segmentation layer with uint32 or uint64 the segment id 2 ** 32 - 1 is rendered completely white (also overwriting the color layer), as this value is reserved as EMPTY_KEY_VALUE for the cuckoo hashing table.

Discussion in slack

Expected Behavior

The segment should be rendered as usual. To fix this, I propose to set the EMPTY_KEY_VALUE = 0 as 0 means eraser for segmentation layers anyway. But EMPTY_KEY_VALUE = 0 should only be set for the custom color cuckoo hash table, not for the once used for color layers.

Current Behavior

See image above.

Steps to Reproduce the bug

1. Open a dataset with segmentation layer uint32 (e.g. l4_sample)
2. Set the segmentation id manually to 2 ** 32 - 1 = 4294967295 and draw around.
3. The drawn area should be completely white everywhere