If the user has an external SD card set as their default storage
(notably on a Huawei device, like the Huawei Mate 10 Lite), then
PersistentBlobProvider will try to write a file to the SD card, but
would fail to generate a URI for it due to us missing a line in our
FileProvider setup. This just adds that missing entry.
Special thanks to @aleb2000 for digging into this!
Fixes#8144Fixes#7726