In `get_post_class()`, ensure that we always coerce the class list passed to the function to an array, even when it's empty.

This is consistent with `get_body_class()`, see [18176].

See #34452.

git-svn-id: https://develop.svn.wordpress.org/trunk@35399 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/post-template.php

@@ -429,6 +429,9 @@ function get_post_class( $class = '', $post_id = null ) {
 			$class = preg_split( '#\s+#', $class );
 		}
 		$classes = array_map( 'esc_attr', $class );
+	} else {
+		// Ensure that we always coerce class to being an array.
+		$class = array();
 	}
 
 	if ( ! $post ) {