[BUGFIX] Fix method getPageParrent in workspace mode

The method "getPageParent($page)" in "FluidTYPO3\Fluidpages\Service\PageService" runns into troubles if "BackendUtility::getLiveVersionIdOfRecord" returns a valid value (WorkspaceId). The solution is more complicated than the first look, cause the Method "getPage()" alway returns a workspace-version (if possible), but in this case the live-version is needed.