crash - add plugin after restart

[PrometheusPi]

@BeyondEspresso just informed me that some plugins crash if they are activated after a restart.
E.g. if the binEnergy plugin is not called via the command line flag picongpu ... --bin_e.period 100 ..., before the restart, but after the restart the plugin is called, the plugin tries to read previous data files, which do not exist, and crashes.

The following plugins are affected:

• BinEnergyParticles
• CountParticles
• EnergyFields
• EnergyParticles

EDIT: All plugins using restoreTxtFile defined in txtFileHandling.hpp are affected.

[ax3l]

great catch, my bad. introduced in #636 since I did not realize such a case can exist, too.

[PrometheusPi]

solved with pull request #703