bug: incorrect display of `eza -T --absolute /full/path`

Version: v0.18.15 [+git]

```bash
~/tmp/20240516 22:05:52$ mkdir -p a/b/c/d

# this output is OK
~/tmp/20240516 22:06:00$ eza -TD --absolute a
/users/xxx/tmp/20240516/a
└── /users/xxx/tmp/20240516/a/b
└── /users/xxx/tmp/20240516/a/b/c
└── /users/xxx/tmp/20240516/a/b/c/d

# this one is NOT - path repeated twice in the root dir
~/tmp/20240516 22:06:21$ eza -TD --absolute $PWD/a
/users/xxx/tmp/20240516//users/xxx/tmp/20240516/a
└── /users/xxx/tmp/20240516/a/b
└── /users/xxx/tmp/20240516/a/b/c
└── /users/xxx/tmp/20240516/a/b/c/d
```

Reproduce the two `eza -TD --absolute` commands from the issue, comparing a relative path with `$PWD/a`. Trace the absolute-path formatting and identify why the root path is duplicated only for the already-absolute argument. Done means the absolute invocation displays the same correctly rooted tree without repeating the path.

Written by the indexing model from the issue text.