Fix crash when loading the stats page

Changelog.md

@@ -8,6 +8,7 @@ This file holds the changelog for Pepperminty Wiki. This is the master list of t
  - Display returnto URL above the login form if present to further mitigate CSRF issues
 
 ### Fixed
+ - Stats: Fix crash when loading the stats page
  - [security] Fixed an XSS vulnerability in the `format` GET parameter of the `stats` action (thanks, @JamieSlome)
  - [security] Ensured that the `returnto` GET parameter leads you only to another place on your Pepperminty Wiki instance (thanks, @JamieSlome)
  - [security] Ensure that Javascript in SVGs never gets executed (it's too challenging to strip it, since it could be lurking in many different places - according to [this answer](https://stackoverflow.com/a/68505306/1460422) even Inkscape doesn't strip all Javascript when asked to)

modules/feature-stats.php

@@ -33,7 +33,7 @@ register_module([
 			global $settings, $statistic_calculators;
 			
 			$allowed_formats = [ "html", "json" ];
-			$format = slugify($_GET["format"]) ?? "html";
+			$format = slugify($_GET["format"] ?? "html");
 			
 			if(!in_array($format, $allowed_formats)) {
 				http_response_code(400);