[BUGFIX] TypoScriptParser does not validate absPath

GeneralUtility::getFileAbsFileName() returns a blank string for
invalid paths.
TypoScriptParser::includeDirectory() does not check the return value,
but passes it on to TypoScriptParser::getAllFilesAndFoldersInPath().
This causes the method to enumerate all entries of /.

Fix this by properly checking the return value of getFileAbsFileName().

Resolves: #58102
Releases: 6.2
Change-Id: I778ad6bfc9d4a6a08f36fdd6ae00ccb9a8d2c03e
Reviewed-on: https://review.typo3.org/29607
Reviewed-by: Johannes Kasberger
Tested-by: Johannes Kasberger
Reviewed-by: Stefan Neufeind
Tested-by: Wouter Wolters
Reviewed-by: Wouter Wolters
Reviewed-by: Markus Klein
Tested-by: Markus Klein