When minimizing round-trips, each cluster returns its own independent
search response. In case sort by field and/or field collapsing were
requested, when one cluster has no results to return, the information
about the field that sorting was based on (SortField array) as well as
the field (and the values) that collapsing was performed on are missing
in the search response. That causes problems as we can't build the
proper `TopDocs` instance which would need to be either `TopFieldDocs`
or `CollapseTopFieldDocs`. The merge routine expects that all the top
docs are of the same exact type which can't be guaranteed. Given that
the problematic results are empty, hence have no impact on the final
results, we can simply skip them.

Closes elastic#40067