Before this commit if a product template has no image, no image was
displayed in the website shop for the product

After this commit if a product template has no image, the image of the
first variant is displayed in the website shop

https://github.com/odoo/odoo/issues/52463



closes odoo/odoo#62431

X-original-commit: 643c8a9d
Signed-off-by: Jérémy Kersten (jke) <jke@openerp.com>