Initialization of extra restart fields

[ukmo-juan-castillo]

Describe the bug
In a previous issue the possibility of writing extra fields in the restart file was added to the code. By default, when running a OASIS coupled configuration, the fields that are sent to other models is always written to the restart file.

The problem happens when no extra fields are requested and no coupling takes place, as in this case the flags indicating if extra restart is taking place is not explicitly initialized. It is assumed that these flags are implicitly set to .FALSE., but this is not always the case, causing that some of the oasis send variables may be initialized to zero, and generating non-reproducible results.

To Reproduce
Steps to reproduce the behavior:
This behaviour has been discovered after comparing the ww3_tp2.16/work_MPI_OMPH regtests of two branches, the WW3 develop and the fb_coupling fields. Although the results are the same, the out_pnt.ww3 file is different, containing values of 0.0 and 1000.0 (the expected value) for the variable ICEF, respectively.

Expected behavior
The flags indicating extra restart fields should be set to .FALSE. explicitly and modified only in the two cases described before: when oasis coupling takes place, or when the user specifies extra restart fields; in this way there will be no unexpected difference in the output fields and the results will always be reproducible.

Screenshots
If applicable, add screenshots to help explain your problem.

Additional context
Add any other context about the problem here.