Avoid NPR in SET (#3115)

android/app/src/main/java/com/reactnativenavigation/views/sharedElementTransition/SharedElements.java

         Iterator<String> iterator = toElements.keySet().iterator();
         while (iterator.hasNext()) {
             String key = iterator.next();
-            if (!ViewVisibilityChecker.check(toElements.get(key))) {
+            if (!ViewVisibilityChecker.check(toElements.get(key)) && fromElements.get(key) != null) {
                 iterator.remove();
                 fromElements.get(key).show();
             }