Query: Prevent PHP notice when get_post_type_object() returns null in is_post_type_archive().

This changeset avoids potential PHP notices caused by `get_post_type_object()` returning `null` when called inside `is_post_type_archive()`.

Props sean212, costdev.
Fixes #56287.


git-svn-id: https://develop.svn.wordpress.org/trunk@54464 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-query.php

@@ -3935,6 +3935,10 @@ class WP_Query {
 		}
 		$post_type_object = get_post_type_object( $post_type );
 
+		if ( ! $post_type_object ) {
+			return false;
+		}
+
 		return in_array( $post_type_object->name, (array) $post_types, true );
 	}