Don't return unavailable renditions

RenditionServiceImpl.getRendition(doc, renditionName) may return unusable renditions because it calls RenditionServiceImpl.getAvailableRenditionDefinition(doc, renditionName) which fails to call RenditionDefinitionRegistry.canUseRenditionDefinition(renditionDefinition, doc).

This is also visible through CMIS as it calls RenditionService.getRendition(doc, renditionName.