fix(sdk): add null reference check
fix(sdk): add null reference check

Add a null reference check also for actualRightController in
VRTK_SDKManager::SetupControllers().

Innoactive/IA-unity-VR-toolkit-VRTK,TMaloteaux/SteamVR_Unity_Toolkit,mattboy64/SteamVR_Unity_Toolkit,gpvigano/SteamVR_Unity_Toolkit,thestonefox/VRTK,virror/VRTK,adamjweaver/VRTK,Fulby/VRTK,gomez-addams/SteamVR_Unity_Toolkit,thestonefox/SteamVR_Unity_Toolkit,gpvigano/VRTK,red-horizon/VRTK