Fix upsampling with constant z (#720)

* Fix upsampling with constant z

* Update Changelog.md

Author: jstriebel

webknossos/Changelog.md

@@ -19,6 +19,7 @@ For upgrade instructions, please check the respective *Breaking Changes* section
 ### Changed
 
 ### Fixed
+- Fixed upsampling with constant z in certain anisotropic cases. [#720](https://github.com/scalableminds/webknossos-libs/pull/720)
 
 
 ## [0.9.23](https://github.com/scalableminds/webknossos-libs/releases/tag/v0.9.23) - 2022-05-03

webknossos/webknossos/dataset/layer.py

@@ -924,7 +924,7 @@ def upsample(
             finest_mag_with_fixed_z = finest_mag.to_list()
             finest_mag_with_fixed_z[2] = from_mag.to_list()[2]
             finest_mag = Mag(finest_mag_with_fixed_z)
-            voxel_size = self.dataset.voxel_size
+            voxel_size = None
         else:
             raise AttributeError(
                 f"Upsampling failed: {sampling_mode} is not a valid UpsamplingMode ({SamplingModes.ANISOTROPIC}, {SamplingModes.ISOTROPIC}, {SamplingModes.CONSTANT_Z})"