Themes: Avoid undefined variable warning on get_svg_filters().

This change fixes an undefined variable warning thrown when `duotone` color setting was set to null in Block Themes `theme.json` file.

Follow-up to [52768].

Props aliakseyenkaihar, audrasjb, rafiahmedd.
Merges [52791] to the 5.9 branch.
Fixes #55241.

Built from https://develop.svn.wordpress.org/branches/5.9@53009


git-svn-id: https://core.svn.wordpress.org/branches/5.9@52598 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-theme-json.php

@@ -1598,6 +1598,7 @@ public function get_svg_filters( $origins ) {
 		$blocks_metadata = static::get_blocks_metadata();
 		$setting_nodes   = static::get_setting_nodes( $this->theme_json, $blocks_metadata );
 
+		$filters = '';
 		foreach ( $setting_nodes as $metadata ) {
 			$node = _wp_array_get( $this->theme_json, $metadata['path'], array() );
 			if ( empty( $node['color']['duotone'] ) ) {
@@ -1606,7 +1607,6 @@ public function get_svg_filters( $origins ) {
 
 			$duotone_presets = $node['color']['duotone'];
 
-			$filters = '';
 			foreach ( $origins as $origin ) {
 				if ( ! isset( $duotone_presets[ $origin ] ) ) {
 					continue;

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9.3-alpha-53008';
+$wp_version = '5.9.3-alpha-53009';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.