It’s a reloaded, alternative comic panel, which would have appeared on page 2 ->

https://derpibooru.org/2124745?q=artist%3Aculu-bluebeaver

So: The original idea was to keep things more save between these two which seemed quite reasonable at first.

However: Since Starlight is so skilled with magic, and very powerful, I’m pretty sure now, she could easily use her magic for birth control, so there is no need for a condom. That also explains why Starlight uses this particular “recruiting-strategy” (which you see in this comic) so free of any worries. Her magic enables her to be in full control of the situation.