Suggest to change orbit_number init to 0 instead of 99999

[TAlonglong]

Code Sample, a minimal, complete, and verifiable piece of code

I suggest using init orbit 0 here https://github.com/pytroll/pytroll-pps-runner/blob/main/nwcsafpps_runner/l1c_processing.py#L95 , as this is the orbit_number initialized in https://github.com/foua-pps/level1c4pps/blob/master/level1c4pps/__init__.py#L383

Else you get mismatch between orbit number used in netcdf filenames and posttroll message orbit_number