fix: Don't allow moving past last line, fixes #30, #24

Off by 1 error

helix-core/src/movement.rs

@@ -45,7 +45,7 @@ pub fn move_vertically(
 
     let new_line = match dir {
         Direction::Backward => row.saturating_sub(count),
-        Direction::Forward => std::cmp::min(row.saturating_add(count), text.len_lines() - 1),
+        Direction::Forward => std::cmp::min(row.saturating_add(count), text.len_lines() - 2),
     };
 
     // convert to 0-indexed, subtract another 1 because len_chars() counts \n