Author settings can be wiped out if global features are toggled

[leonidasmi]

For the Yoast SEO settings fields in the user's profile, we show them only when the respective feature is enabled. In order:

• we show the Title to use for Author page and Meta description to use for Author page fields only when the Enable author archives setting is enabled
• we show the Do not allow search engines to show this author's archives in search results checkbox only when the Enable author archives setting is enabled
• we show the Disable SEO analysis checkbox only when the SEO analysis feature setting is enabled
• we show the Disable readability analysis checkbox only when the Readability analysis feature setting is enabled
• we show the Disable inclusive language analysis checkbox only when the Inclusive language analysis feature setting is enabled

The problem is that if we populate a field (or check a checkbox) and then we disable the respective global setting and then saved something else in the user profile, those previous saves will be overwritten.

Which means that if we later re-enable the global setting, the user-specific setting will have been forgotten

Steps to replicate

1. Go to a user's profile, while the Yoast SEO settings are the default ones
2. Fill the Title to use for Author page with something (or any of the other user settings, mentioned above)
3. Go to Yoast SEO->Settings->Author archives and disable the Enable author archives (or any of the other respective global settings, mentioned above)
4. Refresh the user's profile and save it again (for a totally unrelated thing, like for example enabling the Show Toolbar when viewing site setting )
5. Go to Yoast SEO->Settings->Author archives and re-enable the Enable author archives setting
6. Refresh the user's profile

What's expected:

• for the Title to use for Author page setting to have its original value persisted

What happens instead:

• the Title to use for Author page setting has no value