Engines are loaded into global name `searx.engines.engines` other applications
such as statistics or the histogram use this global variable to search for
values in their own memories, which can lead to key errors as described in
- https://github.com/searxng/searxng/issues/2988
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>
Closes: https://github.com/searxng/searxng/issues/2988