[fix] simple theme: hide the image if img load fails

Add event listener to query selector::

    '#urls img.image'

From the user point of view, I think it is better to hide the image:
img_load_error.svg is helplful in the image category because it still allows to
select the image. IMO, in the news category, the fact there is a missing image
won't help to choose the links. From a developer point of view, the place holder
is signal that may be the engine needs to be updated (at least give a look). The
browser console should show the same information too, but it requires some
additional steps. [1]

[1] https://github.com/searxng/searxng/pull/610#issuecomment-997640132



Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>