Fixed issue with rightButtons getting ignored in preference for empty Screen buttons (#589)

src/deprecated/platformSpecificDeprecated.android.js

 }
 
 function addNavigatorButtons(screen, sideMenuParams) {
+
   const Screen = Navigation.getRegisteredScreen(screen.screen);
   if (screen.navigatorButtons == null) {
     screen.navigatorButtons = _.cloneDeep(Screen.navigatorButtons);
 function getRightButtons(screen) {
   if (screen.navigatorButtons && screen.navigatorButtons.rightButtons) {
     return screen.navigatorButtons.rightButtons;
+  } else if (screen.rightButtons) {
+    return screen.rightButtons
+  }
+
+  const Screen = Navigation.getRegisteredScreen(screen.screen);
+
+  if (Screen.navigatorButtons && !_.isEmpty(Screen.navigatorButtons)) {
+    return _.cloneDeep(Screen.navigatorButtons);
   }
 
-  return screen.rightButtons;
+  return null;
 }
 
 function addNavigationStyleParams(screen) {