Once a statement is prepared to be committed to WAL, it becomes visible
(in the 'read-committed' isolation level) so it can be added to the
tuple cache. That's why if the statement is rolled back due to a WAL
error, we have to invalidate the cache. The problem is that the function
invalidating the cache (`vy_cache_on_write`) ignores the statement if
it's a DELETE judging that "there was nothing and there is nothing now".
This is apparently wrong for rollback. Fix it.

Closes #10879

NO_DOC=bug fix

(cherry picked from commit d64e29da2c323a4b4fcc7cf9fddb0300d5dd081f)