Fix frame cursor functions ignoring stack

src/frame.rs

@@ -44,11 +44,11 @@ impl Frame {
     }
 
     pub fn cursor(&self) -> Option<Pos> {
-        self.cursor
+        self.cursor.map(|p| self.buffer.global_to_local(p))
     }
 
     pub fn set_cursor(&mut self, pos: Option<Pos>) {
-        self.cursor = pos;
+        self.cursor = pos.map(|p| self.buffer.local_to_global(p));
     }
 
     pub fn show_cursor(&mut self, pos: Pos) {