Previously, in function bring_to_singleQE,
it depends on the path->param_info field to determine if the path
can be taken into consideration since we cannot pass params across
motion node. But this is not enough, for example, an index path's
param_info field might be null, but its orderbyclauses refs some
outer params. This commit fixes the issue by adding more check
for indexpath.

See Github Issue: https://github.com/greenplum-db/gpdb/issues/9733
for details.