Full width TextView not stretched as expected

Bug Report/Asking for Help

# Problem description

Following code snippet (excerpt from modified example code):
```rust
let mut panes = LinearLayout::vertical();

panes.add_child(BoxView::with_full_screen(DummyView));
panes.add_child(TextView::new("© 2018 Gal Anonym")
.with_id("status")
.full_width()
.fixed_height(1));

siv.screen_mut().add_transparent_layer(panes);
```
shows:
While I expect the bottom bar to be extended to maximum screen width. I can't tell whether it's a bug in the code or I don't understand documentation. However, maybe somebody can help.

# Environment

* Operating system: Windows 10
* Backend used: pancurses
* Current locale (run `locale` in a terminal): No such thing in Windows, but my main language is Polish :-)
* Cursive version (from crates.io, from git, ...): 0.9.3-alpha.0