API: kdeplot fails with NaNs.
I think the most sensible thing to do here is to drop NaN's, like histograms do, rather than filling 0's. The table in #8177 should be updated to reflect that NaN's are dropped, can do that myself after 8177 gets merged.

Fixes #8182.
 You beat me to this! Thanks. Could you squash these down to a single commit? I'll update the table in #8177 when I merge that one.
 @TomAugspurger Squashed down to a single commit, should be good.
 Thanks.
