[FIX] http: keep debug mode in rediction

The parameter forward_debug is used to keep the debug mode during redirection.
Previous code was setting the debug to None which is ignored by werkzeug, making
the option useless.

Closes #12107

openerp/http.py

@@ -142,7 +142,7 @@ def local_redirect(path, query=None, keep_hash=False, forward_debug=True, code=3
     if not query:
         query = {}
     if forward_debug and request and request.debug:
-        query['debug'] = None
+        query['debug'] = ''
     if query:
         url += '?' + werkzeug.url_encode(query)
     if keep_hash: