[SBE][sharding] invariant failure: no 'tsSlot' during resharding_oplog_sync_agg_*.js

[js_test:resharding_oplog_sync_agg_assert_min_oplog] [jsTest] ----

[js_test:resharding_oplog_sync_agg_assert_min_oplog] [jsTest] Run aggregation pipeline on oplog with $_requestReshardingResumeToken set

[js_test:resharding_oplog_sync_agg_assert_min_oplog] [jsTest] ----

[js_test:resharding_oplog_sync_agg_assert_min_oplog] 

[js_test:resharding_oplog_sync_agg_assert_min_oplog] d20770| 2021-04-06T19:17:58.193+00:00 F  -        23079   [conn1] "Invariant failure","attr":{"expr":"tsSlot","file":"src/mongo/db/query/sbe_stage_builder_coll_scan.cpp","line":212}

[js_test:resharding_oplog_sync_agg_assert_min_oplog] d20770| 2021-04-06T19:17:58.193+00:00 F  -        23080   [conn1] "\n\n***aborting after invariant() failure\n\n"

[js_test:resharding_oplog_sync_agg_assert_min_oplog] d20770| 2021-04-06T19:17:58.193+00:00 F  CONTROL  4757800 [conn1] "Writing fatal message","attr":{"message":"Got signal: 6 (Aborted).\n"}

        // We will be constructing a filter that needs to see the 'ts' field. We name it 'minTsSlot'

        // here so that it does not shadow the 'tsSlot' which we allocated earlier.

        auto&& [fields, minTsSlots, minTsSlot] = makeOplogTimestampSlotsIfNeeded(

            collection, slotIdGenerator, csn->shouldTrackLatestOplogTimestamp);

        // We should always have allocated a 'minTsSlot', and there should always be a 'tsSlot'

        // already allocated for the existing scan that we created previously.

        invariant(minTsSlot);

        invariant(tsSlot);  // <------ fails