Infinite loop when simplifying

**Describe the bug**
attempting to simplify certain valid math expressions causes mathjs to enter an infinite loop

**To Reproduce**
run `simplify("(1/(x*(y-1)))^(1/(y-1))")` in mathjs demo

Reproduce the issue in the mathjs demo with simplify("(1/(x*(y-1)))^(1/(y-1))"), then trace the simplification path that fails to terminate. The payload names no source file or test; done means this valid expression no longer causes an infinite loop while simplifying.

Written by the indexing model from the issue text.