FIX keep current sampler when dataview changes - v2

[TomDLT]

This is a second attempt to fix the issue described in #420 (which was reverted in #421).

[mvdoc]

This (and probably the previous version too) works with cortex.Volume objects, but not cortex.Vertex. I think this is because samplers exist only for cortex.Volume but not cortex.Vertex objects.

This works fine

vol = cortex.Volume.random("S1", "fullhead")
cortex.webgl.show(vol)

Instead, this keeps spinning on "Loading brain..."

vertex = cortex.Vertex.random("S1")
cortex.webgl.show(vertex)

[TomDLT]

Makes sense, thanks for testing it, I'll see how to fix it.

[TomDLT]

I did reproduce the issue with Vertex, and fixed it by defining an empty method setFilter. It works on my machine, please let me know if this new fix works for you.

[mvdoc]

Nice! I can confirm it works. Thanks!