du: show error for nul names with --files0-from

[cakebaker]

This PR shows an "invalid zero-length file name" error when using printf "\0" | du --files0-from=-. The same error is shown if such a name is listed in the file specified with --files0-from=some-file.

It makes the tests nul-1 and nul-2 in https://github.com/coreutils/coreutils/blob/master/tests/du/files0-from.pl pass.

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/inotify-dir-recreate (passes in this run but fails in the 'main' branch)

[sylvestre]

Indeed:

2024-01-02T15:58:06.2321313Z FAIL: tests/du/files0-from
2024-01-02T15:58:06.2321402Z ==========================
2024-01-02T15:58:06.2321406Z 
2024-01-02T15:58:06.2321495Z du 0.0.23
2024-01-02T15:58:06.2321601Z f-extra-arg...
2024-01-02T15:58:06.2321684Z missing...
2024-01-02T15:58:06.2321800Z minus-in-stdin...
2024-01-02T15:58:06.2321881Z empty...
2024-01-02T15:58:06.2321999Z empty-nonreg...
2024-01-02T15:58:06.2322097Z nul-1...
2024-01-02T15:58:06.2322304Z nul-2...
2024-01-02T15:58:06.2322391Z 1...
2024-01-02T15:58:06.2322469Z 1a...
2024-01-02T15:58:06.2322553Z 2...
2024-01-02T15:58:06.2322894Z files0-from.pl: test 2: stdout mismatch, comparing 2.1 (expected) and 2.O (actual)
2024-01-02T15:58:06.2323050Z --- 2.1	2024-01-02 15:47:45.815355703 +0000
2024-01-02T15:58:06.2323208Z +++ 2.O	2024-01-02 15:47:45.819355669 +0000
2024-01-02T15:58:06.2323315Z @@ -1 +1,2 @@
2024-01-02T15:58:06.2323396Z  0	g
2024-01-02T15:58:06.2323474Z +0	g
2024-01-02T15:58:06.2323552Z 2a...
2024-01-02T15:58:06.2323904Z files0-from.pl: test 2a: stdout mismatch, comparing 2a.1 (expected) and 2a.O (actual)
2024-01-02T15:58:06.2324066Z --- 2a.1	2024-01-02 15:47:45.823355637 +0000
2024-01-02T15:58:06.2324226Z +++ 2a.O	2024-01-02 15:47:45.827355604 +0000
2024-01-02T15:58:06.2324327Z @@ -1 +1,2 @@
2024-01-02T15:58:06.2324411Z  0	g
2024-01-02T15:58:06.2324488Z +0	g
2024-01-02T15:58:06.2324591Z zero-len...
2024-01-02T15:58:06.2324772Z FAIL tests/du/files0-from.pl (exit status: 1)