Fix crash when calling dismissModal before app was launched (#2978)

closes #2966

android/app/src/main/java/com/reactnativenavigation/params/parsers/ScreenParamsParser.java

         result.animateScreenTransitions = new AnimationParser(params).parse();
         result.sharedElementsTransitions = getSharedElementsTransitions(params);
 
-        result.animationType = params.getString(ANIMATION_TYPE, AppStyle.appStyle.screenAnimationType);
+        result.animationType = params.getString(ANIMATION_TYPE, AppStyle.appStyle == null ? "" : AppStyle.appStyle.screenAnimationType);
 
         return result;
     }