Fix flicker when reverting last hunk from the project diff view (#26706)

Closes #26696

Closes #ISSUE

Release Notes:

- git: Fix flicker when reverting last hunk in project diff view

crates/git_ui/src/project_diff.rs

@@ -308,7 +308,7 @@ impl ProjectDiff {
 
     fn handle_editor_event(
         &mut self,
-        _: &Entity<Editor>,
+        editor: &Entity<Editor>,
         event: &EditorEvent,
         window: &mut Window,
         cx: &mut Context<Self>,
@@ -330,6 +330,11 @@ impl ProjectDiff {
             }
             _ => {}
         }
+        if editor.focus_handle(cx).contains_focused(window, cx) {
+            if self.multibuffer.read(cx).is_empty() {
+                self.focus_handle.focus(window)
+            }
+        }
     }
 
     fn load_buffers(&mut self, cx: &mut Context<Self>) -> Vec<Task<Result<DiffBuffer>>> {