Some images getting upsampled during interactive segmentation processing instead of downsampled

[AlexanderGetka-cbica]

When running interactive segmentation, some images take a really, really long time to run.
This happens because these already large images are getting upscaled by a large factor under certain conditions (highly anisotropic spacing).

I expect these images to take a reasonable amount of time by default, or to be forced to do so by the downsampling process we perform, not to take longer than other images.

CaPTk Version
1.8.1

Fix is inbound for this, but the existing PR takes priority for the upcoming alpha release.