dbcommands.cpp::CmdDatasize misleading error message on early break

Issue is:

if (Runner::RUNNER_EOF != state) {

                warning() << "Internal error while reading " << ns << endl;

            }

If you hit a maxSize while iterating, you'll break from the loop in state Runner::Advanced, which is normal but throws a worrying message. This happens during every DEBUG autosplit, and adds noise to the log.

Fix should be pretty trivial.