Use is_wp_error() instead of get_class()

get_class() takes an object as an argument, in case of success the returned value is either string or int, not an object which would generate a PHP Warning.
so instead of get class, is_wp_error(), function can be used to check if it's a wp_error
use is_wp_error instead of get_class
Merge pull request #488 from UmeshSingla/master

Use is_wp_error() function to check if it's a wp error object instead of get_class()