Said statement keeps a reference to erm indirectly, via a topology node pointer, but doesn't keep erm alive. This can result in use-after-free. Furthermore, it allows for vnodes being pulled from under the query's feet, as it is running.
To prevent this, keep the erm alive for the duration of the query.
Also, use `host_id` instead of `node`, the node pointer is not needed really, as the statement only uses the host id from it.
Fixes: #15802Closesscylladb/scylladb#15808
* github.com:scylladb/scylladb:
cql3: mutation_fragments_select_statement: use host_id instead of node
cql3: mutation_fragments_select_statement: pin erm reference
(cherry picked from commit 782c6a208a)
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