accounting_l10n_fr: fix exporting lines with 0 quantities
The fix from 7597c300 (accounting_l10n_fr: don't export lines with 0 quantity in FEC, 2023-03-31) was not 100% correct, lines with a quantity but with an asset price of 0 were still exported.
The fix from 7597c300 (accounting_l10n_fr: don't export lines with 0 quantity in FEC, 2023-03-31) was not 100% correct, lines with a quantity but with an asset price of 0 were still exported.