Several controllers reattached

There is an issue when router is detached while executing animated push transactions.
In this case several routers in backstack have `needsAttach` flag set to true.
Obviously, next `rebindIfNeeded` will attach them all.

I'm gonna push PR with the test and fix.

Start by tracing rebindIfNeeded after a router is detached during animated push transactions, focusing on how needsAttach is set for routers in the backstack. Reproduce the case described in the issue, add the mentioned test, and confirm that rebindIfNeeded no longer attaches every affected router unexpectedly.

Written by the indexing model from the issue text.