Add filename to Match about sysfont

[gmlewis]

I ran across this issue as well. If you install any Google Font, for example, it typically ends up in ${HOME}/.local/sharefonts.
If I List() the fonts, they show up. However, if I try to use one of them, it always provides a substitute because the Family and Name fields are empty.

For example:

$ go run main.go
2022/08/04 20:09:01 Found 108 fonts:
2022/08/04 20:09:01 font #1: Family "", Name "", Filename "/home/glenn/.local/share/fonts/Baloo-Regular.ttf"
2022/08/04 20:09:01 font #2: Family "", Name "", Filename "/home/glenn/.local/share/fonts/BalsamiqSans-Bold.ttf"
2022/08/04 20:09:01 font #3: Family "", Name "", Filename "/home/glenn/.local/share/fonts/BalsamiqSans-BoldItalic.ttf"
2022/08/04 20:09:01 font #4: Family "", Name "", Filename "/home/glenn/.local/share/fonts/BalsamiqSans-Italic.ttf"
2022/08/04 20:09:01 font #5: Family "", Name "", Filename "/home/glenn/.local/share/fonts/BalsamiqSans-Regular.ttf"
2022/08/04 20:09:01 font #6: Family "", Name "", Filename "/home/glenn/.local/share/fonts/BungeeShade-Regular.ttf"
2022/08/04 20:09:01 font #7: Family "", Name "", Filename "/home/glenn/.local/share/fonts/Modak.ttf"
2022/08/04 20:09:01 font #8: Family "", Name "", Filename "/home/glenn/.local/share/fonts/Monoton-Regular.ttf"
2022/08/04 20:09:01 font #9: Family "DejaVu Sans", Name "DejaVu Sans Bold", Filename "/usr/share/fonts/truetype/dejavu/DejaVuSans-Bold.ttf"
...

However, stepping through the code, it makes up a family name based on the filename when doing a search, and therefore compares `"bungeeshade"` (for example) to `""` and doesn't find a match. 

I think it is a simple fix of making up a family name for these files (based on their filename) so that when it comes time to make a match, it doesn't ignore fonts that have no family name.

I'll see if I can put together a PR.