Set GDL90 traffic alert bit always when bearing/distance is not available. #580, #582.

main/traffic.go

@@ -259,6 +259,10 @@ func registerTrafficUpdate(ti TrafficInfo) {
 func isTrafficAlertable(ti TrafficInfo) bool {
 	// Set alert bit if possible and traffic is within some threshold
 	// TODO: Could be more intelligent, taking into account headings etc.
+	if !ti.BearingDist_valid {
+		// If not able to calculate the distance to the target, let the alert bit be set always.
+		return true
+	}
 	if ti.BearingDist_valid &&
 		ti.Distance < 3704 { // 3704 meters, 2 nm.
 		return true