fix: do not process tab key in editor when document is hidden

app/assets/javascripts/views/editor/editor_view.ts

@@ -1198,7 +1198,7 @@ class EditorViewCtrl extends PureViewCtrl<{}, EditorState> {
       element: editor,
       key: KeyboardKey.Tab,
       onKeyDown: (event) => {
-        if (this.note.locked || event.shiftKey) {
+        if (document.hidden || this.note.locked || event.shiftKey) {
           return;
         }
         event.preventDefault();