EDD_HTML_Elements::user_dropdown() assumes selected value isn't an array

[ashleyfae]

Bug Report

Expected behavior

I expect to be able to use user_dropdown() and set selected to an array of user IDs. I expect this because it supports the multiple parameter, which allows you to select multiple users.

Actual behavior

When you pass in an array of user IDs you get this notice:

array_key_exists(): The first argument should be either a string or an integer

This is due to using array_key_exists() with $args['selected'] here: https://github.com/easydigitaldownloads/easy-digital-downloads/blob/master/includes/class-edd-html-elements.php#L343-L357 This fails if $args['selected'] is an array.

Steps to reproduce the behavior

1. Install Discounts Pro.
2. Create a discount and assign it to a user.
3. Save.
4. Notice triggers when the page refreshes.

Information (if a specific version is affected):

PHP Version:

EDD Version (or branch):

WordPress Version:

Any other relevant information: