Provide back compat for $theme->$var where $theme was an array from get_themes() but cast to an object, as had occurred in get_theme_updaes(). see #20173. see #20103.

git-svn-id: https://develop.svn.wordpress.org/trunk@20112 602fd350-edb4-49c9-b593-d223f7449a82

wp-includes/class-wp-theme.php

@@ -292,6 +292,9 @@ final class WP_Theme implements ArrayAccess {
 				return $this->get_theme_root();
 			case 'theme_root_uri' :
 				return $this->get_theme_root_uri();
+			// For cases where the array was converted to an object.
+			default :
+				return $this->offsetGet( $offset );
 		}
 	}