Consider currently dequeued Evaluation's ModifyIndex when determining
its WaitIndex. Normally the Evaluation itself would already be in the
state store snapshot used to determine the WaitIndex. However, since the FSM
applies Raft messages to the state store concurrently with Dequeueing,
it's possible the currently dequeued Evaluation won't yet exist in the
state store snapshot used by JobsForEval.

This can be solved by always considering the current eval's modify index
and using it if it is greater than all of the evals returned by the
state store.

Co-Authored-By: schmichael <michael.schurter@gmail.com>

Co-Authored-By: schmichael <michael.schurter@gmail.com>