PwBaseWorkChain cannot restart if stopped during forces/stress calculation

[bastonero]

If the pw.x routine is stopped (due to e.g. wall-time limit) when computing forces and/or stress, while the scf is converged, the PwBaseWorkChain stops and doesn't restart.

I would suggest to implement a handler that possibly can restart with e.g. electron_maxstep = 0 and scf_must_converge = False in order to compute forces and stress, if they were to be computed from the input (or something similar).