Fix namespace detection for pages in root (#30)

Co-authored-by: Elan Ruusamäe <glen@pld-linux.org>

Author: Miro-Collas

README.md

@@ -20,3 +20,7 @@ Download the latest release from [Tags] page and install the plugin using the
 1. Create an Incoming Webhook on slack: https://api.slack.com/messaging/webhooks#create_a_webhook
 
 2. Enter the webhook into the slacknotifier configuration section in DokuWiki's Configuration Settings
+
+## Root Namespace
+
+To include the root namespace, simply put a `:` in the namespace field in the config.

event/PageSaveEvent.php

@@ -34,6 +34,12 @@ public function getEventType(): ?string
      */
     public function getNamespace(): string
     {
+        // Handle special case of page being in root namespace
+        $pos = strpos($this->id, ':');
+        if ($pos === false) {
+            return ':';
+        }
+
         return explode(':', $this->id, 2)[0];
     }