Fix @turf/isobands issue with ring nesting logic#2925
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When working on removing marchingsquares, I noticed that the output of one of the isobands tests looked a bit strange in both the before and after versions of my change. When looking closer it was incorrectly nesting 'outer' ring polygons inside holes of other polygons. This breaks any donut-shaped bands.
Here's the matrix2 input data
Here's the original output showing the oddly shaped polygons that caught my attention.
Here's the version after the fix, which makes more sense:
