cql3/functions: protect against uninitialized value
cql3/functions: protect against uninitialized value

impl_count_function doesn't explicitly initialize _count, so its correctness
depends on default initialization. Let's explicitly initialize _count to
make the code future proof.

Signed-off-by: Raphael S. Carvalho <1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@scylladb.com>
Message-Id: <20200714162604.64402-1-1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@scylladb.com>

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