Read-only Embedded Restricted font

[100kph]

When Zilla Slab is embedded into a PowerPoint document and reopened in any windows machine that does not have Zilla Slab font installed, you get

This presentation cannot be edited because it contains one or more read-only embedded (restricted) fonts

The fonts are
Zila Slab
Zila Slab Light
Zila Slab Semi Bold

[DIV-on-github]

I suspect that this could be due to an oversight. Specifically, "missing Vendor ID".
I had a go at addressing the issue here: #49
But I guess it is still unresolved.

[DIV-on-github]

BTW, it seems I also added licence information in my proposed patch too. It's a couple of years ago since I did this, but apparently I got it from
https://github.com/mozilla/zilla-slab/blob/master/LICENSE