[BUGFIX] Catch FolderDoesNotExist Exception on links/images

If you have RTE content which have false links/images to files, we
get a FolderDoesNotExistException (FileDoesNotExistException in 6.0).
This should be catched.

Reproduce
* Create content element text
* In RTE change to text mode
* Add <img src="nofile" /> for image
or
* Add <a href="nowhere">link</a> for link
* save

Resolves: #46785
Releases: 6.2, 6.1, 6.0
Change-Id: I7b959825e8e36dc5b1941c9fa411afa321a594fb
Reviewed-on: https://review.typo3.org/21042
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe