Fixing issue in `toJSONObject` function of `Schedule` class.
Fixing issue in `toJSONObject` function of `Schedule` class.

The issue: TimeRanges is null. This might happen if Schedule was constructed with
```c#
public Schedule(int activationLimit) :
```
In which case `TimeRanges` will be null.

ravalum/soomla-unity3d-core,ravalum/soomla-unity3d-core,zentuit/soomla-unity3d-core,zentuit/soomla-unity3d-core,vedi/soomla-unity3d-core,vedi/soomla-unity3d-core,ravalum/soomla-unity3d-core,zentuit/soomla-unity3d-core,noctorus/soomla-unity3d-core,zentuit/soomla-unity3d-core,vedi/soomla-unity3d-core,noctorus/soomla-unity3d-core,noctorus/soomla-unity3d-core,noctorus/soomla-unity3d-core,noctorus/soomla-unity3d-core,vedi/soomla-unity3d-core,ravalum/soomla-unity3d-core,vedi/soomla-unity3d-core,ravalum/soomla-unity3d-core