row_cache: Delete the entry even if invalidation failed
row_cache: Delete the entry even if invalidation failed

Otherwise we will leak it, and region destructor will fail:

row_cache_test: utils/logalloc.cc:1211: virtual logalloc::region_impl::~region_impl(): Assertion `seg->is_empty()' failed.

Fixes regression in row_cache_test.

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