Ignore invalid Resource arrays

[n7studios]

Summary

Return false when using the exist method when the array of resource data is a flat array, which isn't the structure used for any resources in any Plugins since 2022.

Implemented in this PR.

Testing

• testGetByWithInvalidResourceData: Tests that the get_by() function returns false when queried with invalid resource data.
• testExistWithInvalidResourceData: Tests that the exist() function returns false when queried with invalid resource data.

Checklist

• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• Security and Sanitization requirements have been followed
• I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)