The `CFFFont.prototype.data` should contain a `Uint8Array`, however if compilation failed it was being set to a `Stream` instance which will thus fail elsewhere in the font-code.
*Please note:* This was found by code inspection, since I don't have a PDF document that's fixed by this change.
After PR 12563 we're now free to use optional chaining in the worker-thread as well. (This patch also fixes one previously "missed" case in the `web/` folder.)
For the MOZCENTRAL build-target this patch reduces the total bundle-size by `1.6` kilobytes.
*Please note:* I don't really know what I'm doing here, however the patch appears to fix the referenced issue when comparing the rendering with Adobe Reader (with the caveat that I don't speak the language in question).