[Dashboard] Clear Add Panel On App Leave (#94530) (#94633)

* cleared add panel in useEffect cleanup function

src/plugins/dashboard/public/application/top_nav/dashboard_top_nav.tsx

@@ -10,6 +10,7 @@ import { i18n } from '@kbn/i18n';
 import angular from 'angular';
 import React, { useCallback, useEffect, useMemo, useState } from 'react';
 
+import UseUnmount from 'react-use/lib/useUnmount';
 import { useKibana } from '../../services/kibana_react';
 import { IndexPattern, SavedQuery, TimefilterContract } from '../../services/data';
 import {
@@ -114,7 +115,9 @@ export function DashboardTopNav({
         id || DASHBOARD_PANELS_UNSAVED_ID
       );
     }
-    return () => visibleSubscription.unsubscribe();
+    return () => {
+      visibleSubscription.unsubscribe();
+    };
   }, [chrome, allowByValueEmbeddables, dashboardStateManager, savedDashboard]);
 
   const addFromLibrary = useCallback(() => {
@@ -458,6 +461,10 @@ export function DashboardTopNav({
     share,
   ]);
 
+  UseUnmount(() => {
+    clearAddPanel();
+  });
+
   const getNavBarProps = () => {
     const shouldShowNavBarComponent = (forceShow: boolean): boolean =>
       (forceShow || state.chromeIsVisible) && !dashboardStateManager.getFullScreenMode();