I don't think it makes much difference. Sometimes I do it before strength training, and sometimes I do it after. Similarly, I like to do it empty stomach early in the morning too. And later in the afternoon, I go for an actual gym workout.
The important thing is that you should do it regularly because cardio has its own benefits.
Likewise, doing cardio empty stomach aids in losing weight, but you've to look out what you're eating throughout the day for that to work.