Fix crash on clear when scrolled up in history

Fixes #3112.

CHANGELOG.md

@@ -33,6 +33,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Performance bottleneck when clearing colored rows
 - Vague startup crash messages on Windows with WinPTY backend
 - Deadlock on Windows when closing Alacritty using the title bar "X" button (ConPTY backend)
+- Crash on `clear` when scrolled up in history
 
 ## 0.4.0
 

alacritty_terminal/src/grid/mod.rs

@@ -544,6 +544,9 @@ impl<T: GridCell + PartialEq + Copy> Grid<T> {
         let positions = self.lines - iter.cur.line;
         let region = Line(0)..self.num_lines();
 
+        // Reset display offset
+        self.display_offset = 0;
+
         // Clear the viewport
         self.scroll_up(&region, positions, template);