Fix stats redirect

When an unauthenticated user comes to any page they are redirected
to login screen. After they authenticate they are redirected
to the original page. But the # part of the url is ignored.
So we have to use regular query params from the email and
redirect user to the canonical URL later.

[MAILPOET-2554]

lib/AdminPages/Pages/Newsletters.php

@@ -75,6 +75,15 @@ class Newsletters {
   public function render() {
     global $wp_roles; // phpcs:ignore Squiz.NamingConventions.ValidVariableName.NotCamelCaps
 
+    if (isset($_GET['stats'])) {
+      $this->wp->wpSafeRedirect(
+        $this->wp->getSiteUrl(null,
+          '/wp-admin/admin.php?page=mailpoet-newsletters#/stats/' . $_GET['stats']
+        )
+      );
+      exit;
+    }
+
     $data = [];
 
     $data['items_per_page'] = $this->listingPageLimit->getLimitPerPage('newsletters');