fix: ui/menu: Don't allow scrolling past the end of completion

Fixes #472

helix-term/src/ui/menu.rs

@@ -90,13 +90,13 @@ impl<T: Item> Menu<T> {
 
     pub fn move_up(&mut self) {
         // TODO: wrap around to end
-        let pos = self.cursor.map_or(0, |i| i.saturating_sub(1)) % self.options.len();
+        let pos = self.cursor.map_or(0, |i| i.saturating_sub(1)) % self.matches.len();
         self.cursor = Some(pos);
         self.adjust_scroll();
     }
 
     pub fn move_down(&mut self) {
-        let pos = self.cursor.map_or(0, |i| i + 1) % self.options.len();
+        let pos = self.cursor.map_or(0, |i| i + 1) % self.matches.len();
         self.cursor = Some(pos);
         self.adjust_scroll();
     }