Editor: Check that attrs is an array in `WP_Block_Supports::apply_b…

…lock_supports()`.

This prevents a fatal error in `wp_apply_custom_classname_support()`, which expects an array data type for block attributes, and makes sure the block editor can still load if there is a mistake in the attributes of a block.

Follow-up to [54498].

Props caercam.
Fixes #61151.

git-svn-id: https://develop.svn.wordpress.org/trunk@58112 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-block-supports.php

@@ -103,7 +103,7 @@ public function apply_block_supports() {
 			return array();
 		}
 
-		$block_attributes = array_key_exists( 'attrs', self::$block_to_render )
+		$block_attributes = array_key_exists( 'attrs', self::$block_to_render ) && is_array( self::$block_to_render['attrs'] )
 			? self::$block_to_render['attrs']
 			: array();