Not able to render EXT:...images with fluid in backend context

[baschny]

This is a similar issue than was already reported by @derhansen in #55.

We hit the same situation (also hard to figure out what the problem was) not in the Install Tool but by calling a scheduler task in the backend when having filefill enabled and a configured login.loginLogo. EXT:brofix's task tries to send an Email using FluidEmail. I end up with:

Execution of task "Execute console commands (scheduler)" failed with the following message:
PHP Warning: sha1_file(typo3conf/ext/sitepackage/Resources/Public/Icons/logo-sign.svg): failed to open stream:
No such file or directory in /app/html/typo3/sysext/core/Classes/Resource/Driver/LocalDriver.php line 751

Even more simple to reproduce. Add something like this to the fluid template of your Backend Module:

<f:image src="EXT:sitepackage/Resources/Public/Icons/logo.svg" absolute="1" alt="TYPO3 Logo" height="41" width="150" />

Seems like the FileFillDriver::getAbsolutePath misses prefixing a site prefix (absoluteBasePath = null for the "pseudo-storage = 0" in this situation).