Untwine aborts when not run in single file mode

[wonder-sk]

On the current main branch, untwine is broken when not used with the single file option.

Previously if I would run

untwine -i file.las -o /tmp/output

and things would work fine, but now it errors out like this:

terminate called after throwing an instance of 'pdalboost::filesystem::filesystem_error'
  what():  pdalboost::filesystem::create_directory: No such file or directory: "/tmp/output/temp"
Aborted (core dumped)

The error happens since this commit: 4271d14

It looks like untwine first tries to create /tmp/output/temp directory before creating /tmp/output ?