Strengthen the download toolbar visible condition just like main.js

fix brave#3758
fix brave#7033

Auditors: @bbondy

Test Plan:

1. Toggle clear download history when close Brave
2. Download something to make download tool bar shows
3. Quit Brave when downloading
4. After relaunch brave go to https://github.com/brave/browser-laptop/issues
5. Search something on filter to make autofill popup
6. The popup shouldn't be shifted

js/contextMenus.js

@@ -1404,7 +1404,8 @@ function onShowUsernameMenu (usernames, origin, action, boundingRect,
 
 function onShowAutofillMenu (suggestions, boundingRect, frame) {
   const menuTemplate = autofillTemplateInit(suggestions, frame)
-  const downloadsBarOffset = windowStore.getState().getIn(['ui', 'downloadsToolbar', 'isVisible']) ? getDownloadsBarHeight() : 0
+  const downloadsBarOffset = windowStore.getState().getIn(['ui', 'downloadsToolbar', 'isVisible']) &&
+    appStore.state.get('downloads') && appStore.state.get('downloads').size ? getDownloadsBarHeight() : 0
   const offset = {
     x: (window.innerWidth - boundingRect.clientWidth),
     y: (window.innerHeight - boundingRect.clientHeight)