DERSL: Only render slides if there are results in the assoc. category

We don't want to display empty slides for things--that will just annoy
viewers of the presentation as they have to wait after each event to see
a blank slide labeled SPECIAL HONORS (or whatever the non-existent honor
is). Besides, we could get crazy NPEs or logic errors from exposing
empty data structures to our slide-generating logic...best we keep the
logic safely shielded from non-existent data.