Spectrum.gauss_fit sometimes return negative FWHM

Spectrum.gauss_fit sometimes return negative FWHM values, as can be shown in the code below with the attached neg_fwhm.fits file. This is a regression that has been introduced in mpdaf 2.3.

#!/usr/bin/python

from mpdaf.obj import Spectrum

spe = Spectrum('neg_fwhm.fits')
l = 5400.5615
flux = 79.165398
g = spe.gauss_fit(l-5, l+5 , lpeak=l, flux=flux, plot=False, weight=False)
print(g.lpeak, g.fwhm)