This strikes me as a little funny.
By my thinking this is always going to be the same value, because this bit of code: https://github.com/basho/bitcask/blob/develop/src/bitcask_nifs.erl#L263-L280 should guarantee that if the pending keydir exists this fold will block until it has completed, so frozen fun (by my reckoning at least) will always be called when `PendingEpoch =:= undefined`.
If I am correct, this PR could be simplified significantly.