Fixed not restarting correctly after import

This is the same as 72a8e0f3b622641f9e6e9ff6001f12db87d9c948
but that commit got lost when merging master into develop

app/src/main/java/de/danoeh/antennapod/fragment/preferences/ImportExportPreferencesFragment.java

@@ -186,6 +186,7 @@ public class ImportExportPreferencesFragment extends PreferenceFragmentCompat {
             ComponentName cn = intent.getComponent();
             Intent mainIntent = Intent.makeRestartActivityTask(cn);
             startActivity(mainIntent);
+            Runtime.getRuntime().exit(0);
         });
         d.show();
     }