NA's in cognostics turn into errors in Table Sort/Filter and Univariate plots

[lhsego]

NA's for any cognostic cause the entire Table Sort/Filter view to throw an error, and it also causes the Univarite Filter to fail for that particular cognostic. Would be nice to add the following functionality:

When the cognostic function is applied in makeDisplay(), run some quick check over the resulting cognostics list, and if there are NA's, remove them from the list before passing them on to the display (so they never appear in the display), and issue a warning or note to the user explaining why the cognostic is not present in the viewer.