[BUGFIX] Avoid exception on trailing comma in include_static_file.txt

If an entry in the include_static_file.txt file contains a trailing
comma, a RuntimeException (1651137904) is thrown. The problem is a
check whether the path contains 'EXT:', in this case the second path
is an empty string and hence the exception is thrown.

The change removes empty strings when splitting the entries in the
file by comma.

Resolves: #102659
Releases: main, 12.4
Change-Id: Ic2290b0b153487c7e982b4bca6b220a6bb9abf55
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82121


Tested-by: Benni Mack <benni@typo3.org>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benni Mack <benni@typo3.org>