then you will be just fine. don't sweat it as long as the first one was sanitized. and even if it wasnt a keg stored at keezer temps/serving temps will be too cold for any opportunistic infection to take off.
I did this in my Maibock when I was kegging it about 2 months. At first mild panic set in then I just figured to let it be and see what would happen. We are about 1/2 way though the keg and have not noticed any problems with it. Just go to show: RDWHAHB/