cache_streamed_mutation: Read static row with cache region locked
cache_streamed_mutation: Read static row with cache region locked

_snp->static_row() allocates and needs reference stability.
Message-Id: <578f10e88bf1b056c6ea89d3b97f0da43d727b9a@scylladb.com>

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