Can a water leak cause a fire in a light fixture?
Chances are the ceiling is damp and you'll be fine. However, I have never been a fan of water and electricity at the same time. With the breaker  switched off, take the globe, glass off the fixture. Water probably wouldn't be in the junction box but could have dripped between the box and the ceiling. If there is any dampness, dry everything off. Put the fixture back together and operate the light as usual... the heat will dry out the ceiling.