row_cache: fix clearing continuity flag at eviction
row_cache: fix clearing continuity flag at eviction

In original implementation the continuity flag indicated that cache has
full information about the range the between current partition and the
one following it, hence when evicting an entry the one preceeding it
had to have its continuity flag cleared.

This was changed, however, and now the continuiy flag tells whether the
cache is continuous between the current element and the one before it.
This means that eviction code needs to clear the flag for the entry
directly following the evicted one.

Signed-off-by: Paweł Dziepak <e29bb3265626c60caf76d587cabdfcd8b379ef80@scylladb.com>

duarten/scylla,raphaelsc/scylla,raphaelsc/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,raphaelsc/scylla,duarten/scylla,scylladb/scylla