Submitted by hansfriese
https://github.com/code-423n4/2023-02-malt/blob/main/contracts/RewardSystem/RewardThrottle.sol#L660 
https://github.com/code-423n4/2023-02-malt/blob/main/contracts/RewardSystem/RewardThrottle.sol#L139
Average APRs might be calculated wrongly after calling populateFromPreviousThrottle() and targetAPR might be changed unexpectedly.
The epoch state struct contains cumulativeCashflowApr element and cashflowAverageApr is used to adjust targetAPR in updateDesiredAPR() function.
And populateFromPreviousThrottle() is an admin function to change activeEpoch and the relevant epoch state using the previous throttle.
And the activeEpoch is likely to be increased inside this function.
The problem might occur when epoch < _activeEpoch + smoothingPeriod because state[epoch].cumulativeCashflowAprand state[epoch - smoothingPeriod].cumulativeCashflowApr will be used for cashflowAverageApr calculation.
So cumulativeCashflowApr of the original epoch and the newly added epoch will be used together and cashflowAverageApr might be calculated wrongly.
As a result, targetAPR might be changed unexpectedly.
Recommend checking epoch - _activeEpoch > smoothingPeriod in populateFromPreviousThrottle().
0xScotch (Malt) confirmed
