Send modal lifecycle events only if modal is not destroyed (#1166)

fixes #1162

android/app/src/main/java/com/reactnativenavigation/controllers/Modal.java

 
     @Override
     public void dismiss() {
-        NavigationApplication.instance.getEventEmitter().sendScreenChangedEvent("willDisappear", layout.getCurrentScreen().getNavigatorEventId());
-        NavigationApplication.instance.getEventEmitter().sendScreenChangedEvent("didDisappear", layout.getCurrentScreen().getNavigatorEventId());
+        if (!isDestroyed) {
+            NavigationApplication.instance.getEventEmitter().sendScreenChangedEvent("willDisappear", layout.getCurrentScreen().getNavigatorEventId());
+            NavigationApplication.instance.getEventEmitter().sendScreenChangedEvent("didDisappear", layout.getCurrentScreen().getNavigatorEventId());
+        }
         super.dismiss();
     }