We do actually use a fallback font, but don't ship that font, so you are still sunk. I have changed the fallback font to Source Code Pro which we do ship with. It's a monospaced font so either that's a good or bad thing! Look forward to this in your next release.
Of course you could always use Awami Nastaliq for your font (not forgetting to turn on Graphite in the font box). It has Latin in it.