A fix to prevent division by zero during normalization

[hightower8083]

I have recently added import_from_lasy and export_to_lasy methods in axiprop and for the latter one I have used an empty profile to get it's field rewritten, i.e.:

wavelength = 2 * np.pi * c / Container.omega0
empty_longitudinal_profile = LongitudinalProfile(wavelength=wavelength)
empty_transverse_profile = TransverseProfile()
empty_profile = CombinedLongitudinalTransverseProfile(
    wavelength=wavelength,
    pol=polarization,
    laser_energy=0.0,
    long_profile=empty_longitudinal_profile,
    trans_profile=empty_transverse_profile,
)

With this I've noticed that the normalization forced at initialization of CombinedLongitudinalTransverseProfile divides field by 0.0, and generates the corresponding warning. Although my methods work fine with this (None field values are overwritten anyway), I don't like this warning.

So this PR checks the energy before normalization and skips it if field is zero.

[ax3l]

LGTM - thanks a lot!

[MaxThevenet]

IIRC, we (in particular @RemiLehe) discussed offline and suggested that the check could be in Laser.normalize, or maybe in each normalize_... in utils. I don't remember what we concluded, but IMO the latter is good so the check is really performed where needed, regardless on how we wrap or call the normalize_.... That way, we shouldn't need to change laser.py.

[RemiLehe]

I updated the PR according to the above comment.

[MaxThevenet]

Looks good, thanks!