This was caused by trying to not show dynamic-svgs that had already been
downloaded when the option to not allow the media-library was activated
(eg in the website logo, we do not want to allow dynamic SVGs)

Unfortunately the domain was doing a string comparison to make sure the
url wasn't like the one from dynamic SVGs but implicitly required that
the url field be not null. This commit fixes that by explicitly allowing
images with a null url field.

task-2466819
part of odoo/odoo#66732

closes odoo/odoo#67411

X-original-commit: 0784e14d
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>