Unable to load Arabic Google Font #424

Hi, first of all thanks for this super useful library. We've been using it in production at BeFunky for several years now with minimal issues.

I'm currently struggling to get Web Font Loader to detect that Almarai, an Arabic Google Font without a Latin subset, has loaded. Here's a pen illustrating the issue:
https://codepen.io/pranksinatra/pen/qBdRxax

The font is loaded (as reflected visually on the page), but WebFontLoader fires the fontinactive callback.

I tried setting testStrings to a value copied from the Google Fonts page for Almarai, assuming that this font at least contains these characters, but it's not working. Any ideas?