Raise DivisionByZeroError when calls to rank result in division by zero

[anth-volk]

This is linked to PolicyEngine/policyengine-uk#928. In situations where a sim or microsim attempts to use the MicroSeries class's rank method with an array of weights that equal 0, microdf should raise an error. This is because the rank method will attempt to divide by the sum of all values within the weights array, be unable to divide, and return an array of nan values.