Default bounding box invalid on datasets if too close to beginning or end of dataset

[boergens]

For example in this dataset:
https://webknossos.org/links/4lUL-u1WDxMcEU8R
I create an annotation, I create a bounding box, but as soon as I go in to edit the bounding box the input field turns red because the bounding box is in fact too big in Z for the current position. If I fix the z extent manually all is good