Administration: Handle the result of Plugin_Upgrader::bulk_upgrade() for a plugin that is already at the latest version in the same way it is handled for themes.

This corrects a fragile check of the result in `wp_ajax_update_plugin()` that depended on the internal array pointer, and brings some consistency with `wp_ajax_update_theme()`.

Follow-up to [37714], [48401].
See #50448.

git-svn-id: https://develop.svn.wordpress.org/trunk@48445 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/class-plugin-upgrader.php

@@ -391,8 +391,8 @@ class Plugin_Upgrader extends WP_Upgrader {
 
 			unset( $past_failure_emails[ $plugin ] );
 		}
+
 		update_option( 'auto_plugin_theme_update_emails', $past_failure_emails );
-		reset( $results );
 
 		return $results;
 	}