magetno 2.3.3 - do not call method on bool value

[mjankiewicz]

Resolve the problem with Magento 2.3.3

[cebesoft]

Not sure if this commit solves the source of this problem: $this->helperData->getRichsnippetsConfig('model_value') should return the attribute configured in seo/general/richsnippets/model_value (from etc/config.xml if config is not saved through backend yet). But acutally this method returns seo/richsnippets/model_value which is empty.