Ensure polar spaces during roundtrip have undefined hues for achromatic

This changes nothing but simply adds testing to confirm

Author: facelessuser

tests/test_roundtrip.py

@@ -107,6 +107,9 @@ def test_round_trip(self, space):
 
         for c in self.COLORS:
             self.assert_round_trip(c, space)
+            if c._space.is_polar():
+                hue = c._space.hue_name()
+                assert math.isnan(c[hue]) is True
 
 
 class TestRYBRoundTrip(TestRoundTrip):