[BUGFIX] FileStorageExtractionTask breaks if file not found

Before the file is processed a extra check is done to be sure the file
exists. If the file doesn't exist it's marked as missing.

Resolves: #80061
Releases: master, 8.7
Change-Id: Ifda396b75d2ace0ce126057a4e118856b15c05e0
Reviewed-on: https://review.typo3.org/51969


Reviewed-by: Frans Saris <franssaris@gmail.com>
Tested-by: Frans Saris <franssaris@gmail.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Thomas Hohn <thomas@hohn.dk>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>