Conditional on select with no value matches is and is-after

Create a select component and create a conditional which uses IS or IS AFTER as the operator. Have no default. When the webform is initially displayed and before a radio button is selected, the conditionals will be true. They should be false.

For reasons that aren't clear to me now, I defined NULL as less than any value. I think the result of that should be NULL, rather than 1 or -1 in webform_compare_select() and the jQuery equivalent for intra-page conditionals.