Fix favoriting guide during reload

1. Reload guide
1. Favorite guide before the guide is retrieved
1. Crash

Invalidating the menu fixes it because it disables the menu if
`mGuide == null`. I also added a guard around `mGuide.isFavorited()`
just in case.
Fix favoriting then reloading the guide

1. Favorite a guide
1. Reload the guide
1. Favorite API call returns
1. Crash.
1. Guide API call returns

Guarding the `mGuide.setFavorited(favorited)` call fixes it.