Blender Git Loki

Fix Asset Browser showing oudated list for changes done while browser is hidden

Steps to reproduce were:
* Open an Asset Browser
* "Mark Asset" on some data-block
* Change the Asset Browser into a different editor (not File Browser!)
* "Clear Asset" on the data-block again, or mark another asset
* Change back to the Asset Browser, it will show an outdated list

Now the file-browser reloads local file data after spaces were changed. Note
that the current notifier code doesn't limit the space-change notifiers to the
affected spaces, so changing any visible space will trigger this. That's an
issue to be fixed separately.