[Unreal] Fix crash when simulating pathing.

The Steam Audio Probe Volume actor that the Steam Audio Source component points to
via TSoftObjectPtr ended up different from the Probe Volume actor that
BeginPlay gets called on, so an invalid IPLProbeBatch ended up getting
passed to the simulator.

Fixes: #265

unreal/src/SteamAudioUnreal/Plugins/SteamAudio/Source/SteamAudio/Private/SteamAudioSourceComponent.cpp

@@ -67,7 +67,7 @@ void USteamAudioSourceComponent::SetInputs(IPLSimulationFlags Flags)
     {
         Inputs.flags = static_cast<IPLSimulationFlags>(Inputs.flags | IPL_SIMULATIONFLAGS_REFLECTIONS);
     }
-    if (bSimulatePathing && PathingProbeBatch.IsValid())
+    if (bSimulatePathing && PathingProbeBatch)
     {
         Inputs.flags = static_cast<IPLSimulationFlags>(Inputs.flags | IPL_SIMULATIONFLAGS_PATHING);
     }
@@ -106,7 +106,7 @@ void USteamAudioSourceComponent::SetInputs(IPLSimulationFlags Flags)
 
     if (PathingProbeBatch)
     {
-        Inputs.pathingProbes = PathingProbeBatch.Get()->GetProbeBatch();
+        Inputs.pathingProbes = PathingProbeBatch->GetProbeBatch();
     }
 
     Inputs.bakedDataIdentifier = GetBakedDataIdentifier();

unreal/src/SteamAudioUnreal/Plugins/SteamAudio/Source/SteamAudio/Public/SteamAudioSourceComponent.h

@@ -128,7 +128,7 @@ class STEAMAUDIO_API USteamAudioSourceComponent : public UActorComponent
 
     /** The probe volume within which to simulate pathing. Only if simulating pathing. */
     UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = PathingSettings)
-    TSoftObjectPtr<ASteamAudioProbeVolume> PathingProbeBatch;
+    ASteamAudioProbeVolume* PathingProbeBatch;
 
     /** If true, baked paths are checked for occlusion by dynamic geometry. Only if simulating pathing. */
     UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = PathingSettings)