🪲 Fix error page (#5612)

The error page was failing because it was trying to retrieve an image that wasn't there.

Fixes #5598

**How to test**

Follow these steps to verify this PR works as intended:

* Go to http://127.0.0.1:5000/hedy/a24e2453366248fb9359fffa3089d209/view whilst logged out and see that the image and the message is shown.

templates/error-page.html

@@ -3,7 +3,7 @@
 {% block regular_content %}
   <div class="flex flex-col items-center">
       <div class="w-1/2 mt-8">
-          <img class="w-full" src="/images/{{ error }}.png" alt="{{_('error_logo_alt')}}">
+          <img class="w-full" src="/images/{{ error_image }}.png" alt="{{_('error_logo_alt')}}">
       </div>
       <div class="mb-6 -mt-8 text-lg font-bold">
           {{page_error}}

utils.py

@@ -329,8 +329,10 @@ def error_page(error=404, page_error=None, ui_message=None, menu=True, iframe=No
     if error not in [400, 403, 404, 500, 401]:
         error = 404
     default = gettext('default_404')
+    error_image = error
     if error == 401:
         default = gettext('default_401')
+        error_image = 403
     if error == 403:
         default = gettext('default_403')
     elif error == 500:
@@ -347,8 +349,8 @@ def error_page(error=404, page_error=None, ui_message=None, menu=True, iframe=No
                               "error": default,
                               "exception": traceback.format_exception(type(exception), exception, exception.__traceback__) if exception else None}, error)
 
-    return render_template("error-page.html", menu=menu, error=error, iframe=iframe,
-                           page_error=page_error or ui_message or '', default=default), error
+    return render_template("error-page.html", menu=menu, error_image=error_image, iframe=iframe,
+                           page_error=page_error or ui_message or default or '', default=default), error
 
 
 def session_id():