fix(sliceview): tweak sliceview chunk priority formula again
fix(sliceview): tweak sliceview chunk priority formula again

Fixes the problem introduced by commit c21f6919946ba60909f434dfb74098a5b09f0c5f of mesh/skeleton
chunks having lower priority than sliceview chunks.

seung-lab/neuroglancer,seung-lab/neuroglancer,google/neuroglancer,google/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,google/neuroglancer,seung-lab/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,seung-lab/neuroglancer,seung-lab/neuroglancer,google/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,seung-lab/neuroglancer,seung-lab/neuroglancer,janelia-flyem/neuroglancer