fix(decor): unwrap if max width fits 0 chars

The `title_pixmap` function assumed if `title` was not empty, the returned
`glyphs` from `layout_title_glyphs` would also not be empty.
`layout_title_glyphs`, however, could break before a single insertion if
`max_width` was too small. Emacs, when using `emacsclient
--create-frame`, could call `title_pixmap` with a `max_width` of 1,
causing a panic. Closes #311.

src/server/decoration.rs

@@ -382,8 +382,7 @@ fn title_pixmap(title: &str, max_width: u32, height: u32, scale: f32) -> Option<
 
     let width = glyphs
         .last()
-        .map(|g| g.position.x + font.h_advance(g.id))
-        .unwrap()
+        .map(|g| g.position.x + font.h_advance(g.id))?
         .ceil() as u32;
 
     let mut pixmap = Pixmap::new(width, height).unwrap();