[IMP] l10n_in_edi_ewaybill: added error handling for error code 4026

Handled error for if e-waybill is already generated and we send request for
e-way bill generation it will give error -
[4026] Duplicate e-waybill for the given document.

Fix - It will fetch the ewaybill details and shows the ewaybill has been already
      generated

task-3262244

closes odoo/odoo#120829

X-original-commit: 886536ce
Signed-off-by: Xavier Dollé (xdo) <xdo@odoo.com>