Autonav speed fixes

This is pretty simple:

- Fixes a problem where time wouldn't slow down for non-enemy hostiles.
- If the slider is at a shield level, time doesn't slow down unless you tood damage this frame, but then it keeps slowing down for a couple seconds after that.
- Enemies aren't considered to be present unless they are seen for two consecutive frames. This works around the weird problem where you would get single-frame slowdowns, which was very annoying.