Does not work with File Based Encryption (FBE)

[Beneter]

Hi,

this is an awesome project! Please do not abandon it...

Description:
When backing up a device with File Based Encryption (FBE) the userdata and media of of users != 0 is not backed up.

Steps To Reproduce:

1. Use a Device with FBE
2. Create at least one additional user
3. Run the Backup

Result:
The APK is being backed up correctly, but only the userdata and media of the fist user (0) is being backed up.
There is no error message.

Expected Result:
The software should either be able to decrypt FBE of other users, or at least throw an error message when FBE is detected (getprop ro.crypto.type = file).