Plugins: Return the original value in `apply_filters_deprecated()` if no filter is registered for the tag.

Props flixos90.
Fixes #10441.

git-svn-id: https://develop.svn.wordpress.org/trunk@37911 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/plugin.php

@@ -674,7 +674,7 @@ function remove_all_actions($tag, $priority = false) {
  */
 function apply_filters_deprecated( $tag, $args, $version, $replacement = false, $message = null ) {
 	if ( ! has_filter( $tag ) ) {
-		return;
+		return $args[0];
 	}
 
 	_deprecated_hook( $tag, $version, $replacement, $message );

tests/phpunit/tests/filters.php

@@ -359,4 +359,13 @@ class Tests_Filters extends WP_UnitTestCase {
 
 		return $p1;
 	}
+
+	/**
+	 * @ticket 10441
+	 */
+	public function test_apply_filters_deprecated_without_filter() {
+		$val = 'Foobar';
+
+		$this->assertSame( $val, apply_filters_deprecated( 'tests_apply_filters_deprecated', array( $val ), '4.6' ) );
+	}
 }