Allow negentropy sync with broad filters

NoEmptyFilters was blocking negentropy sessions that send
filters without kinds/authors/ids. Skip the check for
negentropy sessions so strfry and other tools can sync.

main.go

@@ -161,7 +161,12 @@ func main() {
 	)
 
 	relay.OnRequest = policies.SeqRequest(
-		policies.NoEmptyFilters,
+		func(ctx context.Context, filter nostr.Filter) (reject bool, msg string) {
+			if khatru.IsNegentropySession(ctx) {
+				return false, ""
+			}
+			return policies.NoEmptyFilters(ctx, filter)
+		},
 		policies.NoComplexFilters,
 	)