sstables: Make variadic write() not picked on substitution error
sstables: Make variadic write() not picked on substitution error

If write(v, out, x) doesn't match any overload, the variadic write()
will be picked, with Rest = {}. The compiler will print error messages
about unable to find write(v, out), which totally obscures the
original cause of mismatch.

Make it picked only when there are at least two write() parameters so
that debugging compilation errors is actually possible.

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