[BUGFIX] Catch exception in element browser

If the last selected folder doesn't exist anymore an exeption in the
element browser was thrown.

Resolves: #52306
Releases: 6.2, 6.1, 6.0
Change-Id: Ia6645fd61b879ecaedd98f7f7fa17bd3dd7c162b
Reviewed-on: https://review.typo3.org/24842
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter