incorrect error "unsupported btrfs-progs" reported after failed send

A send failed, probably due to a network failure, and btrbk reports `ERROR: Failed to parse subvolume detail (unsupported btrfs-progs)`. But as far as I can tell, the error had nothing to do with that. The next run of btrbk, it says "Target subvolume xxx exists
, but is not a receive target of yyy." and "Please delete stray subvolumes", that made more sense. Here is a bigger excerpt from the logs:

```
Mar 01 22:00:26 kd sysd-mail-once[1851213]: Checking for missing backups of subvolume "/mnt/o/o" in "x3wg.b8.nz:/mnt/o/btrbk/"
Mar 01 22:00:26 kd sysd-mail-once[1851213]: Creating incremental backup...
Mar 01 22:00:26 kd sysd-mail-once[1851213]: [send/receive] target: x3wg.b8.nz:/mnt/o/btrbk/o.20230301T210018-0500
Mar 01 22:00:26 kd sysd-mail-once[1851213]: [send/receive] source: /mnt/o/btrbk/o.20230301T210018-0500
Mar 01 22:00:26 kd sysd-mail-once[1851213]: [send/receive] parent: /mnt/o/btrbk/o.20230301T190008-0500
Mar 01 22:00:26 kd btrbk[1851213]: send-receive starting ssh://x3wg.b8.nz/mnt/o/btrbk/o.20230301T210018-0500 /mnt/o/btrbk/o.20230301T210018-0500 /mnt/o/btrbk/o.20230301T190008-0500 -
Mar 01 22:01:02 kd sysd-mail-once[1851213]: [send/receive] checking target metadata: x3wg.b8.nz:/mnt/o/btrbk/o.20230301T210018-0500
Mar 01 22:01:05 kd sysd-mail-once[1851213]: ERROR: Failed to parse subvolume detail (unsupported btrfs-progs)s for: x3wg.b8.nz:/mnt/o/btrbk/o.20230301T210018-0500
Mar 01 22:01:05 kd sysd-mail-once[1851213]: ERROR: Failed to send/receive subvolume: /mnt/o/btrbk/o.20230301T210018-0500 [/mnt/o/btrbk/o.20230301T190008-0500] -> x3wg.b8.nz:/mnt/o/btrbk/o.20230301T210018-0500
Mar 01 22:01:05 kd sysd-mail-once[1851213]: ERROR: ... SSH command failed (exitcode=255)
Mar 01 22:01:05 kd sysd-mail-once[1851213]: ERROR: ... sh: btrfs send -p '/mnt/o/btrbk/o.20230301T190008-0500' '/mnt/o/btrbk/o.20230301T210018-0500' | ssh -i '/q/root/h' root@x3wg.b8.nz 'btrfs receive '\''/mnt/o/btrbk/'\'''
Mar 01 22:01:05 kd sysd-mail-once[1851213]: ERROR: ... client_loop: send disconnect: Broken pipe
Mar 01 22:01:05 kd sysd-mail-once[1851213]: ERROR: ... failed to read stream from kernel: Broken pipe
Mar 01 22:01:05 kd sysd-mail-once[1851213]: ERROR: ... failed to check target subvolume: x3wg.b8.nz:/mnt/o/btrbk/o.20230301T210018-0500
Mar 01 22:01:05 kd sysd-mail-once[1851213]: ERROR: ... cannot find real path for '/mnt/o/btrbk/o.20230301T210018-0500': No such file or directory
Mar 01 22:01:05 kd btrbk[1851213]: send-receive ERROR ssh://x3wg.b8.nz/mnt/o/btrbk/o.20230301T210018-0500 /mnt/o/btrbk/o.20230301T210018-0500 /mnt/o/btrbk/o.20230301T190008-0500 -
Mar 01 22:01:05 kd sysd-mail-once[1851213]: ERROR: Error while resuming backups, aborting
Mar 01 22:01:05 kd sysd-mail-once[1851213]: Created 0/2 missing backups
```

btrbk run again an hour later

```
Mar 01 23:00:23 kd sysd-mail-once[1930563]: Checking for missing backups of subvolume "/mnt/o/o" in "x3wg.b8.nz:/mnt/o/btrbk/
"
Mar 01 23:00:23 kd sysd-mail-once[1930563]: WARNING: Target subvolume "x3wg.b8.nz:/mnt/o/btrbk/o.20230301T210018-0500" exists
, but is not a receive target of "/mnt/o/btrbk/o.20230301T210018-0500"
Mar 01 23:00:23 kd sysd-mail-once[1930563]: WARNING: Please delete stray subvolumes: "btrbk clean x3wg.b8.nz:/mnt/o/btrbk"
Mar 01 23:00:23 kd sysd-mail-once[1930563]: WARNING: Skipping backup of: /mnt/o/btrbk/o.20230301T210018-0500
```