"Fixes #2734."
* 'tgrabiec/make-sstable-reader-work-with-empty-range-set' of github.com:scylladb/seastar-dev:
tests: Introduce clustering_ranges_walker_test
tests: simple_schema: Add missing include
sstables: reader: Make clustering_ranges_walker work with empty range set
clustering_ranges_walker: Make adjacency more accurate
(cherry picked from commit 5224ab9c92)