Fix a possible null reference bug

briar-android/src/main/java/org/briarproject/briar/android/keyagreement/KeyAgreementActivity.java

@@ -177,7 +177,7 @@ public abstract class KeyAgreementActivity extends BriarActivity implements
 		// FIXME #824
 		FragmentManager fm = getSupportFragmentManager();
 		if (fm.findFragmentByTag(KeyAgreementFragment.TAG) == null) {
-			BaseFragment f = KeyAgreementFragment.newInstance(this);
+			BaseFragment f = KeyAgreementFragment.newInstance();
 			fm.beginTransaction()
 					.replace(R.id.fragmentContainer, f, f.getUniqueTag())
 					.addToBackStack(f.getUniqueTag())

briar-android/src/main/java/org/briarproject/briar/android/keyagreement/KeyAgreementFragment.java

@@ -91,15 +91,19 @@ public class KeyAgreementFragment extends BaseEventFragment
 	private KeyAgreementTask task;
 	private KeyAgreementEventListener listener;
 
-	public static KeyAgreementFragment newInstance(
-			KeyAgreementEventListener listener) {
+	public static KeyAgreementFragment newInstance() {
 		Bundle args = new Bundle();
 		KeyAgreementFragment fragment = new KeyAgreementFragment();
-		fragment.listener = listener;
 		fragment.setArguments(args);
 		return fragment;
 	}
 
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+		listener = (KeyAgreementEventListener) context;
+	}
+
 	@Override
 	public void injectFragment(ActivityComponent component) {
 		component.inject(this);