[fix] googel engine - "some results are invalids: invalid content"

Fix google issues listet in the `/stats?engine=google` and message::

    some results are invalids: invalid content

The log is::

    DEBUG   searx                         : result: invalid content: {'url': 'https://de.wikipedia.org/wiki/Foo

', 'title': 'Foo - Wikipedia', 'content': None, 'engine': 'google'}
    WARNING searx.engines.google          : ErrorContext('searx/search/processors/abstract.py', 111, 'result_container.extend(self.engine_name, search_results)', None, 'some results are invalids: invalid content', ()) True

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