ThrottledUnfilteredIterator failed on UnfilteredRowIterator with only partition level info

// create cell tombstone, range tombstone, partition deletion
createTable("CREATE TABLE %s (pk int, ck1 int, ck2 int, v1 int, v2 int, PRIMARY KEY (pk, ck1, ck2))");
// partition deletion
execute("DELETE FROM %s USING TIMESTAMP 160 WHERE pk=1");

// flush and generate 1 sstable
ColumnFamilyStore cfs = Keyspace.open(keyspace()).getColumnFamilyStore(currentTable());
cfs.forceBlockingFlush();
cfs.disableAutoCompaction();
cfs.forceMajorCompaction();

assertEquals(1, cfs.getLiveSSTables().size());
SSTableReader reader = cfs.getLiveSSTables().iterator().next();

try (ISSTableScanner scanner = reader.getScanner();
        CloseableIterator<UnfilteredRowIterator> throttled = ThrottledUnfilteredIterator.throttle(scanner, 100))
{
    assertTrue(throttled.hasNext());
    UnfilteredRowIterator iterator = throttled.next();
    assertFalse(throttled.hasNext());
    assertFalse(iterator.hasNext());
    assertEquals(iterator.partitionLevelDeletion().markedForDeleteAt(), 160);
}