[BUGFIX] InvalidXmlFileException for invalid locallang.xml

Throw a meaningful InvalidXmlFileException when an invalid locallang.xml
file is detected.

Resolves: #79908
Releases: master, 7.6
Change-Id: Idc5586166d2475edeaeef407128525ea57fb9a09
Reviewed-on: https://review.typo3.org/51761


Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Tested-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Thomas Hohn <thomas@hohn.dk>
Reviewed-by: Anders Kostending <aha@systime.dk>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Faton Haliti <fha@systime.dk>
Tested-by: Faton Haliti <fha@systime.dk>
Reviewed-by: Helmut Hummel <typo3@helhum.io>
Tested-by: Helmut Hummel <typo3@helhum.io>