streamer: use direct object for filter checks when there is no valid child object...

streamer: use direct object for filter checks when there is no valid child object in an activity

We call Object.normalize/1 to get the child object for situations like Announce.
However, the check is flawed and immediately fails if Object.normalize/1 fails.
Instead, we should use the activity itself in those cases to allow activities which
never have a child object to pass through the filter.

Closes #1291