[FIX] web_editor: traceback on saving the product
[FIX] web_editor: traceback on saving the product

before this commit: when creating a product from frontend and editing
the product and delete image and save edition, it throws traceback,
because ir.qweb.field.image doesn't get any url and due to which it
throws traceback.

after this commit: if url is not defined in ir.qweb.field.image field
converter then return None

task-2063293

closes odoo/odoo#40638

X-original-commit: 896127a6528fa59f7f385019e296acd5db585321
Signed-off-by: Jérémy Kersten (jke) <56923a0c9ca793c07ff1df1013de5694062a27a6@openerp.com>

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo