Publicize: Mitigate obscure PHP fatals when REST receives malformed data

[tbradsha]

Closes MONOREP-133

This should address the following:

PHP Fatal error: Uncaught TypeError: array_map(): Argument #2 ($array) must be of type array, string given in /wordpress/plugins/jetpack/15.1/jetpack_vendor/automattic/jetpack-publicize/src/rest-api/class-share-post-controller.php:72

PHP Fatal error: Uncaught TypeError: array_map(): Argument #2 ($array) must be of type array, string given in /wordpress/plugins/jetpack/15.1-a.11/jetpack_vendor/automattic/jetpack-publicize/src/class-rest-controller.php:109

We're not quite sure how this is occurring, as validate_callback should be catching things before it gets here, but this fix should be safe enough, returning an empty array if the param is not an array.

More discussion here: p1759441599526559-slack-C08PN0LHCCT

Proposed changes:

Other information:

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Testing instructions:

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[github-actions]

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 2 files.

File	Coverage	Δ%	Δ Uncovered
projects/packages/publicize/src/class-rest-controller.php	125/220 (56.82%)	-1.59%	6 💔
projects/packages/publicize/src/rest-api/class-share-post-controller.php	46/75 (61.33%)	-3.88%	5 💔

Full summary · PHP report · JS report

_{If appropriate, add one of these labels to override the failing coverage check: Covered by non-unit tests Use to ignore the Code coverage requirement check when E2Es or other non-unit tests cover the code Coverage tests to be added later Use to ignore the Code coverage requirement check when tests will be added in a follow-up PR I don't care about code coverage for this PR Use this label to ignore the check for insufficient code coveage.}

[manzoorwanijk]

It should ideally return an error in this case.

[tbradsha]

081bcdf

[manzoorwanijk]

Thank you for this.