When the generational mode cannot add any old regions to a mixed collection because they are _all_ pinned, it gives up trying to evacuate these regions. The regions must then be made parsable. However, if this phase is interrupted by a young collection it should no longer try to evacuate any old regions. Doing so triggered an assert when testing with `-XX:ShenandoahCoalesceChance=80` and `XX:+ShenandoahAllocFailureALot`.