Uncaught TypeError: array_key_exists when testing

[michailf]

Prerequisites

Please answer the following questions for yourself before submitting an issue. YOU MAY DELETE THE PREREQUISITES SECTION.

• [ x] I am running the latest version
• [ x] I checked the documentation and found no answer
• [ x] I checked to make sure that this issue has not already been filed

Expected Behavior

Test should give a result

Current Behavior

Test gives no result

Steps to Reproduce

1. Create a configuration with a cleanup section that uses a single string.
2. Create a test configuration with a cleanup section that now has an array of strings.

Failure Logs

``` Uncaught TypeError: array_key_exists(): Argument #2 ($array) must be of type array, string given in /var/www/html/tt-rss/plugins.local/feediron/init.php:716 Stack trace: #0 /var/www/html/tt-rss/plugins.local/feediron/init.php(718): Feediron->arrayRecursiveDiff() #1 /var/www/html/tt-rss/plugins.local/feediron/init.php(762): Feediron->arrayRecursiveDiff() #2 /var/www/html/tt-rss/classes/pluginhandler.php(15): Feediron->test() #3 /var/www/html/tt-rss/backend.php(137): PluginHandler->catchall() #4 {main} thrown ```

[dugite-code]

Thanks for opening the issue. Good catch, should be a fairly simple fix