it's hard to see from the picture, but gas escaping through a tiny crack doesn't strike me as a massive issue. It's also possible that your previous fermentation didn't produce co2 vigorously enough to disturb the airlock. The point of an airlock is to allow the co2 escape while preventing anything from getting in, but the co2 creates a natural blanket and outward pressure that typically protects the beer so a little escaping though a crack, if that's the case, shouldn't cause any harm.
Is the crack just on the rim? Like, a place where the beer would not contact it? My big concern with any crack in a fermenter is that is provides a place for infectious agents to hide. I'm sure if you're aware of it and your sanitation process is thorough, the location of the crack is nothing to be concerned about.
Hope this was helpful.