cleanup: sub 4k again

src/view/chain.rs

@@ -9,11 +9,20 @@ pub struct ChainView<'a> {
 }
 
 impl<'a> ChainView<'a> {
+    pub fn horizontal (app: &'a App) -> Self {
+        Self::new(app, false)
+    }
+    pub fn vertical (app: &'a App) -> Self {
+        Self::new(app, true)
+    }
     pub fn new (app: &'a App, vertical: bool) -> Self {
         Self {
+            vertical,
             focused:  app.section == AppSection::Chain,
-            track:    app.tracks.get(app.track_cursor - 1),
-            vertical
+            track:    match app.track_cursor {
+                0 => None,
+                _ => app.tracks.get(app.track_cursor - 1)
+            },
         }
     }
 }