[!!!][BUGFIX] Throw exception on invalid charset

This gives users a clear hint if e.g. config.metaCharset contains
an invalid value instead of showing a blank page.

Change-Id: I9cdb37cc7e61af10e2d1985ef43f488e53b17a48
Resolves: #82852
Releases: master, 8.7
Reviewed-on: https://review.typo3.org/54471


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Reviewed-by: Wolfgang Klinger <wolfgang@wazum.com>
Tested-by: Riccardo De Contardi <erredeco@gmail.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>