All the large data handler methods rely on global qctx thing to
write down its notes. This creates circular dependency:
query processor -> database -> large_data_handler -> qctx -> qp
In scylla this is not a technical problem, neither qctx nor the
query processor are stopped. It is a problem in cql_test_env
that stops everything, including resetting qctx to null. To avoid
tests stepping on nullptr qctx add the explicit check.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
75e1d7ea74