On the converged attribute from built-in networks

[christian-cahig]

In the following snippet,

from pandapower.networks import case1888rte

net = case1888rte()

we have

>> print(net.res_bus)
Empty DataFrame
Columns: [vm_pu, va_degree, p_mw, q_mvar]
Index: []

>> print(net.res_line)
Empty DataFrame
Columns: [p_from_mw, q_from_mvar, p_to_mw, q_to_mvar, pl_mw, ql_mvar, i_from_ka, i_to_ka, i_ka, vm_from_pu, va_from_degree, vm_to_pu, va_to_degree, loading_percent]
Index: []

>> print(net.converged)
True

That net.res_bus and net.res_line are empty dataframes is expected behavior, since we have not called any computation of result parameters. However, I believe setting net.converged to True is unexpected behavior. In general, I think net.converged should be True or False only after any computation involving result parameters. I am leaning towards a default value of None.