Partial results from shard queries needlessly discarded for queries without sort fields

SOLR-9882 introduced a behavior change in handing partial results from a shard when a timeout occurs. If a shard returns partial results and an empty sortValues, then all the results for a shard are discarded.  For a scoring query the sortValues is empty, so partial results results are never included in the merged results. If all shards timeout, then zero results are returned.

Co-incidentally, in some timeout scenarios sortValues is null. This was recently addressed in SOLR-14758, but that code is impacted by the proposed change, which is to set sortValues to an empty list if is null and to no longer skip merging the shard results when sortValues is empty and the shard results are partial. There may be necessary changes further down in the merge phase when sortValues are missing, partial results are returned and the sortSpec expects sortValues.