Crash doing clean install on latest commit

[jacobgkau]

Distribution (run cat /etc/os-release): Pop!_OS 21.10

Related Application and/or Package Version (run apt policy $PACKAGE NAME): distinst 0.3.2~1635024578~21.10~404fc73 (404fc73)

Issue/Bug Description: Getting a crash when attempting to do a default, encrypted install:

INFO distinst:crates/disks/src/config/partitions/mod.rs:118] obtaining partition information from /dev/nvme0n1p1
[INFO distinst:crates/disks/src/config/partitions/mod.rs:118] obtaining partition information from /dev/nvme0n1p2
[INFO distinst:crates/disks/src/config/partitions/mod.rs:118] obtaining partition information from /dev/nvme0n1p3
[INFO distinst:crates/disks/src/config/partitions/mod.rs:118] obtaining partition information from /dev/nvme0n1p4
[INFO distinst:crates/disks/src/config/disk.rs:348] specifying to write new table on /dev/nvme0n1
[INFO distinst:crates/disks/src/config/disk.rs:278] unmount all partitions on /dev/nvme0n1
[DEBUG distinst:crates/disk-types/src/sector.rs:17] get block size for "/sys/class/block/nvme0n1"
[INFO distinst:crates/disks/src/config/disk_trait.rs:118] checking if 4096:1023999 overlaps
[DEBUG distinst:crates/disk-types/src/sector.rs:17] get block size for "/sys/class/block/nvme0n1"
[INFO distinst:crates/disks/src/config/disk_trait.rs:118] checking if 1024000:9412607 overlaps
[DEBUG distinst:crates/disk-types/src/sector.rs:17] get block size for "/sys/class/block/nvme0n1"
[DEBUG distinst:crates/disk-types/src/sector.rs:17] get block size for "/sys/class/block/nvme0n1"
[INFO distinst:crates/disks/src/config/disk_trait.rs:118] checking if 9412608:460469423 overlaps
[DEBUG distinst:crates/disk-types/src/sector.rs:17] get block size for "/sys/class/block/nvme0n1"
[DEBUG distinst:crates/disk-types/src/sector.rs:17] get block size for "/sys/class/block/nvme0n1"
[DEBUG distinst:crates/disk-types/src/sector.rs:17] get block size for "/sys/class/block/nvme0n1"
[INFO distinst:crates/disks/src/config/disk_trait.rs:118] checking if 460469424:468858031 overlaps
[DEBUG distinst:crates/disk-types/src/sector.rs:17] get block size for "/sys/class/block/nvme0n1"
[DEBUG distinst:crates/disk-types/src/sector.rs:17] get block size for "/sys/class/block/nvme0n1"
Logical device of data is "/dev/mapper/data"
[DEBUG distinst:crates/disk-types/src/sector.rs:17] get block size for "/sys/class/block/data"
[DEBUG distinst:crates/disk-types/src/sector.rs:17] get block size for "/sys/class/block/data"
[DEBUG distinst:crates/disk-types/src/sector.rs:17] get block size for "/sys/class/block/data"
[ERROR distinst:ffi/src/lib.rs:49] libdistinst: pointer in FFI is null
[ERROR distinst:ffi/src/lib.rs:49] libdistinst: pointer in FFI is null
[ERROR distinst:ffi/src/lib.rs:49] libdistinst: pointer in FFI is null
thread '<unnamed>' panicked at 'BlockDeviceExt::get_device_path missing file_name', /build/distinst-oJDGlM/distinst-0.3.2~1635024578~21.10~404fc73/crates/disk-types/src/device.rs:63:14
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
fatal runtime error: failed to initiate panic, error 5
Aborted

Steps to reproduce (if you know):

1. Install distinst from master staging repo.
2. Attempt to perform default clean install with encryption.

Other notes: Checked after seeing @cybik's comment on the commit: 404fc73#commitcomment-58582551

This commit was added in #266 last week.

[cybik]

For the record, no-encryption exhibits the same behaviour.