fix(decor): respect !self.should_draw in set_title

`set_title` would call `update_buffer` at the end of the function, even
if the bar was explicitly not supposed to be drawn (most commonly
because the window had been fullscreened). Since `set_title` is called
outside of the decorations file, a check here made the most sense.

Resolves #310.

src/server/decoration.rs

@@ -235,6 +235,9 @@ impl DecorationsDataSatellite {
 
     pub fn set_title(&mut self, world: &World, title: &str) {
         self.title = Some(title.to_string());
+        if !self.should_draw {
+            return;
+        }
 
         // Don't draw title if there's not enough space
         let title_pixmap = title_pixmap(