Miner.Partition: Check sector existence on expiry and termination

[wadealexc]

1. PopExpiredSectors should check that all sectors popped from the expiration queue exist in the partition:

specs-actors/actors/builtin/miner/partition_state.go

Line 634 in 20ebf9f

expiredSectors, err := bitfield.MergeBitFields(popped.OnTimeSectors, popped.EarlySectors)

2. PopEarlyTerminations should check that all sectors processed in the early termination queue exist in the partition:

specs-actors/actors/builtin/miner/partition_state.go

Lines 753 to 754 in 20ebf9f

	if err = earlyTerminatedQ.ForEach(func(epoch abi.ChainEpoch, sectors bitfield.BitField) error {
	toProcess := sectors