Login screens: fix crash on back navigation

matrix-sdk-android/src/main/java/im/vector/matrix/android/api/auth/AuthenticationService.kt

@@ -47,6 +47,11 @@ interface AuthenticationService {
      */
     fun getRegistrationWizard(): RegistrationWizard
 
+    /**
+     * True when login and password has been sent with success to the homeserver
+     */
+    val isRegistrationStarted: Boolean
+
     /**
      * Cancel pending login or pending registration
      */

matrix-sdk-android/src/main/java/im/vector/matrix/android/internal/auth/DefaultAuthenticationService.kt

@@ -134,6 +134,9 @@ internal class DefaultAuthenticationService @Inject constructor(@Unauthenticated
                 }
     }
 
+    override val isRegistrationStarted: Boolean
+        get() = currentRegistrationWizard?.isRegistrationStarted == true
+
     override fun getLoginWizard(): LoginWizard {
         return currentLoginWizard
                 ?: let {

vector/src/main/java/im/vector/riotx/features/login/LoginViewModel.kt

@@ -70,7 +70,7 @@ class LoginViewModel @AssistedInject constructor(@Assisted initialState: LoginVi
 
     // True when login and password has been sent with success to the homeserver
     val isRegistrationStarted: Boolean
-        get() = registrationWizard?.isRegistrationStarted == true
+        get() = authenticationService.isRegistrationStarted
 
     private val registrationWizard: RegistrationWizard?
         get() = authenticationService.getRegistrationWizard()