Improve support for missing elements.

[sybrew]

From [JS's report](https://wordpress.org/support/topic/using-the_seo_framework_inpost_settings_tabs-typeerror-inputs-ogtitle/:

Add more robustness to the social inputs: If one goes missing, JS should not error.

Fix autodescription/lib/js/social.js to prevent throwing an error for input fields that don’t exist; [e.g., when using filter the_seo_framework_inpost_settings_tabs].