e2c9cdb576 moved the validation of the range tombstone change to the place where it is actually consumed, so we don't attempt to pass purged or discarded range tombstones to the validator. In doing so however, the validate pass was moved after the consume call, which moves the range tombstone change, the validator having been passed a moved-from range tombstone. Fix this by moving he validation to before the consume call.
Refs: #12575Closes#13749
* github.com:scylladb/scylladb:
test/boost/mutation_test: add sanity test for mutation compaction validator
mutation/mutation_compactor: add validation level to compaction state query constructor
mutation/mutation_compactor: validate range tombstone change before it is moved
204521b9a7