[BUGFIX] Catch all errors on adding files of sys_files to export

Adding files from sys_file records is not robust enough. For example
sys_file records could exist for already deleted files. In this case a
RuntimeException is thrown, which is not caught currently.

Solution: catch all Exceptions thrown from Resources in
export_addSysFile and report them to the user.

Resolves: #59015
Releases: master, 6.2
Change-Id: If7ce51a2ae756b43dc30d5545b076310972342f4
Reviewed-on: http://review.typo3.org/30318


Reviewed-by: Frans Saris <franssaris@gmail.com>
Tested-by: Frans Saris <franssaris@gmail.com>
Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>