Reset snackbar action

app/src/main/java/eu/faircode/email/ActivityView.java

@@ -1047,7 +1047,10 @@ public class ActivityView extends ActivityBilling implements FragmentManager.OnB
 
     @Override
     protected void onDestroy() {
+        if (lastSnackbar != null) {
+            lastSnackbar.setAction(null, null);
             lastSnackbar = null;
+        }
         LocalBroadcastManager lbm = LocalBroadcastManager.getInstance(this);
         lbm.unregisterReceiver(creceiver);
         super.onDestroy();