Normally the Catholic Church waits until the previous pope dies before electing his successor.
Agreed. but there have been cases in the past where the Pope resigned (not a lot, obviously).
Given that Benedict resigned, what would you have the Church do? Should they have just not had a Pope until Benedict died? Given that he resigned in 2013, that would have meant that the Church would have been without a Pope for 7 years (and counting).
I submit that the Church had no choice but to elect another Pope when Benedict resigned, and there is precedence for doing so.