Unit function failure due to privacy provider implementation.

[andrewmadden]

Unit test failure:

vendor/bin/phpunit --testsuite tool_log_testsuite --filter test_get_contexts_for_userid``

1) tool_log_privacy_testcase::test_get_contexts_for_userid
Failed asserting that an array is empty.

/var/www/site/admin/tool/log/tests/privacy_test.php:69
/var/www/site/lib/phpunit/classes/advanced_testcase.php:80
phpvfscomposer:///var/www/site/vendor/phpunit/phpunit/phpunit:60

The privacy provider provides the system context regardless if a userid is found in the plugin data here: https://github.com/trax-project/moodle-trax-logs/blob/master/classes/privacy/provider.php#L81

Context should only be added if userid found in actors table.