[BUGFIX] Fix FlashMessage when dumping autoload-information in composer-mode

In composer-mode the autoload-information can't be dumped. A FlashMessage
is shown as a notice. But the message itself was left empty and instead
a message-title was given which is not shown in the backend.

Resolves: #85515
Releases: master
Change-Id: Ie8e59fb5272f1a1682b19652ac991e5dbee6a4e3
Reviewed-on: https://review.typo3.org/57511


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Jan Stockfisch <jan.stockfisch@googlemail.com>
Tested-by: Jan Stockfisch <jan.stockfisch@googlemail.com>
Reviewed-by: Jörg Bösche <typo3@joergboesche.de>
Reviewed-by: Andreas Wolf <andreas.wolf@typo3.org>
Tested-by: Andreas Wolf <andreas.wolf@typo3.org>