LibWeb: Check font family is present to avoid NPD when serializing CSS

[vedant-pandey]

Issue

When serializing CSS with missing Font-Family the current implementation would crash due to a Null Pointer Dereference on missing attribute

Fix

Ensure presence of Font-Family is checked to avoid the occurrence of the NPD

Additional

Refactor comments to stay coherent with the current spec

Fixes: #6259

[Psychpsyo]

I think this also probably warrants a spec bug be filed over at https://github.com/w3c/csswg-drafts/labels/cssom-1, since the spec is telling us to do things that seem impossible.

[AtkinsSJ]

It looks like this got a little bit mangled. Can you please combine this into a single commit as it's a single change, and also correct the comments?

The way to handle the spec being wrong (as it is here) is:

• Keep the spec comments themselves as they are.
• Report a spec issue if there isn't one already.
• Add some // AD-HOC: ... comments of your own to the parts where you had to ignore what the spec currently says.

(I see Cameron has commented already while I was writing this, but I'll keep it anyway for emphasis.)

[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you for your contributions!

[vedant-pandey]

Hi, sorry I was on vacation, will be completing this soon

[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you for your contributions!