views: fix folder/update validation

Validate request parameters before accessing the dictionary values.
Prevent web backtrace.

ogcp/views.py

@@ -1427,12 +1427,12 @@ def action_folder_update():
         return redirect(url_for("scopes"))
     else:
         params = request.args.to_dict()
-        folder_id = int(params.get('folder'))
 
-        if not folder_id:
+        if not 'folder' in params:
             flash(_('Please, select a folder to modify'), category='error')
             return redirect(url_for('scopes'))
 
+        folder_id = int(params.get('folder'))
         scopes, clients = get_scopes()
         folder = find_element_scope(folder_id, 'folder', scopes)
         form.server.data = params['scope-server']