Prevent IllegalStateException when orphaned Fragments try to popBackStack()...

Prevent IllegalStateException when orphaned Fragments try to popBackStack() (EXPOSUREAPP-4430) #1987

* Prevent IllegalStateException if a fragment that's not added to an Activity tries to popBackStack()

* Typo

Corona-Warn-App/src/main/java/de/rki/coronawarnapp/util/ui/FragmentExtensions.kt

@@ -4,7 +4,16 @@ import androidx.fragment.app.Fragment
 import androidx.navigation.NavDirections
 import androidx.navigation.fragment.findNavController
 import de.rki.coronawarnapp.ui.doNavigate
+import timber.log.Timber
 
 fun Fragment.doNavigate(direction: NavDirections) = findNavController().doNavigate(direction)
 
-fun Fragment.popBackStack() = findNavController().popBackStack()
+fun Fragment.popBackStack(): Boolean {
+    if (!isAdded) {
+        IllegalStateException("Fragment is not added").also {
+            Timber.w(it, "Trying to pop backstack on Fragment that isn't added to an Activity.")
+        }
+        return false
+    }
+    return findNavController().popBackStack()
+}