Prevent PHP fatals with robots_txt filter

[tbradsha]

Closes MONOREP-47

If bad data was passed to the robots_txt filter (e.g. null) we'd get a fatal, since the data should be a string. This resets the param to an empty string if it isn't already a string.

I recently became aware of another set of logs to monitor, and this popped up as an easy but important one to fix.

Proposed changes:

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Jetpack product discussion

Does this pull request change what data or activity we track or use?

Testing instructions:

You can probably reproduce with by adding filter, but the code should be pretty straightforward.

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Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/packages/jetpack-mu-wpcom/src/features/blog-privacy/blog-privacy.php	27/35 (77.14%)	1.39%	0 💚

Full summary · PHP report

[anomiex]

Instead of this, we may have to do like

$public = (int) get_option( 'blog_public' );

WordPress 6.8 started casting the value to bool before calling the hook (see WordPress/wordpress-develop@f01e8109), and wpcom picked that up too (see Automattic/wpcom@d84b7196). If we still want to handle the non-Core "-1" case (treating it as "extra-false" rather than true as will be passed) in this hook, we'll need to refetch it.

[tbradsha]

Good catch! Addressed in 49cf5f4.

[anomiex]

Looks reasonable, haven't tested though.

One suggestion for a comment inline

[anomiex]

Looks like there's tests for this code that will need updating now that we re-fetch the option.