AF-14713 saw an invariant failure because we assume isActive is true whenever we yield from FLEMongoDResourceYielder.

However, there is a window of time during beginOrContinue where we our state is kInProgress, but haven't unstashed the txnResources yet (which is where we set isActive = true), so stashing the resources during the yield hits this invariant. (See AF for more details on the timeline of events and code links).

We should skip stashing resources if they were never unstashed (which is indicated by isActive = false).