[BUGFIX] Allow external images for FluidEmail image ViewHelpers

To overcome external images via FluidEmail and apply the similar
behaviour as in LoginController, the <f:image> and <f:uri.image>
ViewHelpers do not process external images but just return them,
allowing logins again with custom login images and "sendNotificationEmail"
settings turned on.

Resolves: #90656
Releases: master
Change-Id: I8ae70da66ee506c085a88690f27d0930b4bfc99d
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63635


Tested-by: Jonas Eberle <flightvision@googlemail.com>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Jonas Eberle <flightvision@googlemail.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>