MOPPAND-1603: Fix for ConductorNavigator getActivity() NPE crash.

Author: ambrose40

app/src/main/java/ee/ria/DigiDoc/android/utils/navigator/conductor/ConductorNavigator.java

@@ -163,6 +163,9 @@ public void removeBackButtonClickListener(BackButtonClickListener listener) {
 
     @Override
     public Activity activity() {
+        if (router == null) {
+            throw new IllegalStateException("Router is null");
+        }
         Activity activity = router.getActivity();
         if (activity == null) {
             throw new IllegalStateException("Activity is null");