Fix XRSound CTD (#658)

[EvESpirit]

Fixes a null pointer dereference that causes XRSound to hard crash the entire simulation if we try to open the hatch, nosecone or retrograde thrusters.

[TheGondos]

This is likely a regression with the removal of CString strings. I'll have a look on my side too.
Edit: OK, so GetWavForAnimationState can return nullptr, then the check in LoadAndPlayWavUsingID for !pWavFile.empty() is useless because it's too late.
It can be fixed in AnimationSoundPreStep::clbkPreStep :

        case AnimationState::StateType::Opening:
        case AnimationState::StateType::Open:
        case AnimationState::StateType::Closing:
        case AnimationState::StateType::Closed:
		{
			const char *wavefile =  m_animationSounds.GetWavForAnimationState(stateType);
			if(wavefile)
	            LoadAndPlayWavUsingID(m_animationSounds.GetOpenCloseSoundID(), wavefile, false, m_animationSounds.GetPlaybackType());
            break;
		}
        case AnimationState::StateType::Moving:
		{
			const char *wavefile =  m_animationSounds.GetWavForAnimationState(stateType);
			if(wavefile)
	            LoadAndPlayWavUsingID(m_animationSounds.GetMovingSoundID(), wavefile, true, m_animationSounds.GetPlaybackType());
            break;
		}

[EvESpirit]

I did that now, thanks.