[ADD] beesdoo_account: _compute_residual() override

`sign` depends on the `amount_total` value

beesdoo_account/models/account_invoice.py

@@ -5,6 +5,18 @@ from odoo.exceptions import UserError
 class AccountInvoice(models.Model):
     _inherit = "account.invoice"
 
+    @api.one
+    @api.depends(
+        'state', 'currency_id', 'invoice_line_ids.price_subtotal',
+        'move_id.line_ids.amount_residual',
+        'move_id.line_ids.currency_id')
+    def _compute_residual(self):
+        super(AccountInvoice,self)._compute_residual()
+        sign = self.amount_total < 0 and -1 or 1
+        self.residual_company_signed *= sign
+        self.residual_signed *= sign
+        self.residual *= sign
+
     @api.multi
     def action_invoice_open(self):
         if self.user_has_groups(