For clarity, initialize some arrays that previously were only assigned via short circuit in loops.

See #30799.


git-svn-id: https://develop.svn.wordpress.org/trunk@30982 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/theme.php

@@ -406,6 +406,7 @@ function search_theme_directories( $force = false ) {
 	$found_themes = array();
 
 	$wp_theme_directories = (array) $wp_theme_directories;
+	$relative_theme_roots = array();
 
 	// Set up maybe-relative, maybe-absolute array of theme directories.
 	// We always want to return absolute, but we need to cache relative