TYPO3 Core

Version 8.4 has a button to toggle the pagetree/filelist tree in the upper left corner;

Steps to reproduce the problem:
1) log in TYPO3
2) Make sure to visualize the "welcome screen" i.e. the screen with the description of the available modules - you can refresh the browser window.
3) click on the button that toggles the pagetree

Result: an empty gray column. So I think that the button should be disabled if you are in the welcome screen.

There are other modules to whom the pagetree has no much sense, and it should be disabled for them too:

- extension manager
- languages
- backend user
- log
- install
- db check
- configuration
- reports
- scheduler