TaggableMultiBackend does not initilaizeBackend leading to errors in use

[kitsunet]

The TaggableMultiBackend does not do $this->initializeBackends() in new methods implemented, this can result in wrong results if the flush is the first thing done with said backend. That can easily be seen if a TaggableMultiBackend is configured for Neos_Fusion_Content and then changes in hte backend are done. Changes that should reload content on apply will not correctly work.