[scudo] Update ring buffer test to make it accept zero size

allocation ring buffer is allowed to be zero. Update the logic in the
test so that on the platform that disables it won't fail this case.

Reviewed By: fmayer

Differential Revision: https://reviews.llvm.org/D144055

GitOrigin-RevId: dfacba5af0fb5dcdbf269b97258e435007276bf1
1 file changed