[YCQL] index update on list after an overwrite has incorrect behavior

[kmuthukk]

Test Case 1:

ycqlsh:k> create table T(k int primary key, l list<int>);
ycqlsh:k> update T set l=[1, 2, 3] where k=1;
ycqlsh:k> update T set l[0]=100 where k=1;
ycqlsh:k> select * from T;

 k | l
---+-------------
 1 | [100, 2, 3]            --> EXPECTED/CORRECT

(1 rows)

# but after an overwrite to list
ycqlsh:k> update T set l=[4, 5, 6] where k=1;

# this statement results in incorrect behavior
ycqlsh:k> update T set l[0]=100 where k=1;
ycqlsh:k> select * from T;

 k | l
---+----------------
 1 | [100, 4, 5, 6]         -->  INCORRECT --> the list should now be [100, 5, 6]

(1 rows)

Test Case 2:

create table test(h int, v list<int>, primary key(h));
insert into test(h,v) values (1, [5,6,7,8]);
update test set v = [1,2,3,4] where h = 1;

-- Should throw an index-out-of-range error, but will succeed because old
-- values are not skipped when searching for the index.
update test set v[6] = 11 where h = 1;

select * from test;

 h | v
---+---------------
 1 | [1, 2, 11, 4]        --> INCORRECT ; the previous UPDATE should have raised an error.