To test this PR run a local instance and try to query page 51:
http://127.0.0.1:8888/search?q=foo&pageno=51
A parameter exception will be raised:
searx.exceptions.SearxParameterException: Invalid value "51" for parameter pageno
And the client will receive a HTTP 400 (Bad request).
Closes https://github.com/searxng/searxng/issues/2972
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>