Formatting: Add type checking to _sanitize_text_fields().

When a non-string value is passed, return an empty string.

Props Mte90.
Fixes #41450.



git-svn-id: https://develop.svn.wordpress.org/trunk@44618 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/formatting/SanitizeTextField.php

@@ -93,6 +93,10 @@ class Tests_Formatting_SanitizeTextField extends WP_UnitTestCase {
 				'Nested octects %%%ABABAB %A%A%ABBB',
 				'Nested octects',
 			),
+			array(
+				array(),
+				'',
+			),
 		);
 	}