IssueTracker

Component used: Navigation
Version used: 2.1.0-alpha03
Devices/Android versions reproduced on:

If you repeat Navigate with URI, the back key does not work.

I'll attach the sample project. Please check below how to reproduction.

1. Tap `MOVE TO A`
2. Tap `MOVE TO B`
3. Tap `MOVE TO D` (Navigate with URI to another nav graph)
4. Press back key.
5. Repeat step 3 and step 4 2 times
6. We can't back to Fragment A.

I think mBackStack is not correct in NavGraphNavigator and NavController.
When step3, NavGraphNavigator#navigate is not called, but NavGraph is added to NavController.mBackStack.

Thanks.