bug: incorrect quotes in `url()`

[bartveneman]

From nldesignsystem.nl:

--ifm-menu-link-sublist-icon: url("data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" width="16px" height="16px" viewBox="0 0 24 24"><path fill="rgba(0,0,0,0.5)" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path></svg>");

If the original string already contains ", do not wrap it in " again.

[bartveneman]

perhaps related: this base64 URl seems to cause chaos:

background-image:url(data:image/svg+xml;base64,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)