Currently, the last mutation emitted by split_mutation could be empty.
It can happen as follows:
- consume range tombstone change at pos `1` with some timestamp
- consume clustering row at pos `2`
- flush: this will create mutation with range tombstone (1, 2) and
clustering row at 2
- consume range tombstone change at pos `2` with no timestamp (i.e.
closing rtc)
- end of partition
since the closing rtc has the same position as the clustering row, no
additional range tombstone will be emitted -- the only necessary range
tombstone was already emitted in the previous mutation.
On the other hand, `test_split_mutations` expects all emitted mutations
to be non-empty, which is a sane expectation for this function.
The test catched a case like this with random-seed=629157129.
Fix this by skipping the last mutation if it turns out to be empty.
Fixes: scylladb/scylladb#18042Closesscylladb/scylladb#18375
1297b9a322