Atomic do not proceed closing with back button on Android

[ivansapr]

If the Atomic page is closed using the Android back button, the activity does not call the onCompletion methods.
The internal _isLoading variable is also set to true.

Steps to reproduce (Android):

1. Call Atomic.transact()
2. Tap back button.
3. Try to call Atomic.transact() again.

ER: Atomic is opened
AR: Nothing happened