Formatting: Add type checking to `_sanitize_text_fields()`.

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

Props Mte90.
Fixes #41450.


Built from https://develop.svn.wordpress.org/trunk@44618


git-svn-id: http://core.svn.wordpress.org/trunk@44449 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/formatting.php

@@ -5102,6 +5102,10 @@ function sanitize_textarea_field( $str ) {
  * @return string Sanitized string.
  */
 function _sanitize_text_fields( $str, $keep_newlines = false ) {
+	if ( ! is_string( $str ) ) {
+		return '';
+	}
+
 	$filtered = wp_check_invalid_utf8( $str );
 
 	if ( strpos( $filtered, '<' ) !== false ) {

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-beta1-44617';
+$wp_version = '5.1-beta1-44618';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.