With normal module, the icon is always loaded from the filesystem but
when importing a module that contains a module icon (by default in
static/description/icon.png) it crash with a `FileNotFound` exceptions
because the image is not available on the filesystem but as an
ir.attachment.
This ensure that for imported module we load the icon from the
corresponding imported attachment
closesodoo/odoo#141133
Signed-off-by: Pierre Masereel (pim) <pim@odoo.com>