Options, Meta APIs: Check if the gmt_offset value is numeric in sanitize_option().

When saving the settings via the admin UI, the default value for any options not passed in the current `$_POST` request is set to `null` in `wp-admin/options.php`. Some options, e.g. `blog_public`, then rely on `null` being passed to `update_option()` to determine whether the value was changed or not.

This commit resolves a PHP 8.1 deprecation notice when saving the `gmt_offset` option without any changes:
{{{
Deprecated: preg_replace(): Passing null to parameter #3 ($subject) of type array|string is deprecated
}}}

Includes a similar fix for the `blog_charset` option.

Follow-up to [4112], [4329], [5541], [21849].

Props adi3890, dhrupo, hrdelwar, hasanmisbah, oglekler, mukesh27, SergeyBiryukov.
Fixes #57728.

git-svn-id: https://develop.svn.wordpress.org/trunk@56132 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-includes/formatting.php

@@ -4883,7 +4883,11 @@ function sanitize_option( $option, $value ) {
 			break;
 
 		case 'blog_charset':
-			$value = preg_replace( '/[^a-zA-Z0-9_-]/', '', $value ); // Strips slashes.
+			if ( is_string( $value ) ) {
+				$value = preg_replace( '/[^a-zA-Z0-9_-]/', '', $value ); // Strips slashes.
+			} else {
+				$value = '';
+			}
 			break;
 
 		case 'blog_public':
@@ -4918,7 +4922,11 @@ function sanitize_option( $option, $value ) {
 			break;
 
 		case 'gmt_offset':
-			$value = preg_replace( '/[^0-9:.-]/', '', $value ); // Strips slashes.
+			if ( is_numeric( $value ) ) {
+				$value = preg_replace( '/[^0-9:.-]/', '', $value ); // Strips slashes.
+			} else {
+				$value = '';
+			}
 			break;
 
 		case 'siteurl':

tests/phpunit/tests/option/sanitizeOption.php

@@ -36,6 +36,7 @@ public function data_sanitize_option() {
 			array( 'blogname', '&lt;i&gt;My Site&lt;/i&gt;', '<i>My Site</i>' ),
 			array( 'blog_charset', 'UTF-8', 'UTF-8' ),
 			array( 'blog_charset', 'charset', '">charset<"' ),
+			array( 'blog_charset', '', null ),
 			array( 'blog_public', 1, null ),
 			array( 'blog_public', 1, '1' ),
 			array( 'blog_public', -2, '-2' ),
@@ -45,6 +46,7 @@ public function data_sanitize_option() {
 			array( 'ping_sites', "http://www.example.com\nhttp://example.org", "www.example.com \n\texample.org\n\n" ),
 			array( 'gmt_offset', '0', 0 ),
 			array( 'gmt_offset', '1.5', '1.5' ),
+			array( 'gmt_offset', '', null ),
 			array( 'siteurl', 'http://example.org', 'http://example.org' ),
 			array( 'siteurl', 'http://example.org/subdir', 'http://example.org/subdir' ),
 			array( 'siteurl', get_option( 'siteurl' ), '' ),