Steps to reproduce:

1. Import the provided Package
2. Select the VFXG_CandleFlamevfx asset and drop it in a Scene.
3. Open the The VFX in a new window.
4. Make sure to get both Scene view window and VFX Graph window active.

Actual results: Notice that the console get spammed with this error and that you cannot fly around in the scene anymore. 

 
{code:java}
NullReferenceException: Object reference not set to an instance of an object.
UnityEngine.Bindings.ThrowHelper.ThrowNullReferenceException (System.Object obj) (at <3cd81afcc40f4cc18fb35505f5fc2eb9>:0)
UnityEngine.Texture.GetDimension () (at <3cd81afcc40f4cc18fb35505f5fc2eb9>:0)
UnityEngine.Texture.get_dimension () (at <3cd81afcc40f4cc18fb35505f5fc2eb9>:0)
UnityEditor.VFX.VFXSlotTexture3D.GenerateErrors (UnityEditor.VFX.VFXErrorReporter report) (at ./Library/PackageCache/com.unity.visualeffectgraph@ce719eb6e6e9/Editor/Models/Slots/Implementations/VFXSlotTexture3D.cs:12)
UnityEditor.VFX.VFXErrorReporter.GenerateErrors () (at ./Library/PackageCache/com.unity.visualeffectgraph@ce719eb6e6e9/Editor/Models/VFXErrorManager.cs:155)
UnityEditor.VFX.VFXErrorManager.GenerateErrors () (at ./Library/PackageCache/com.unity.visualeffectgraph@ce719eb6e6e9/Editor/Models/VFXErrorManager.cs:48)
UnityEditor.VFX.VFXGraph.RecompileIfNeeded (System.Boolean preventRecompilation, System.Boolean preventDependencyRecompilation) (at ./Library/PackageCache/com.unity.visualeffectgraph@ce719eb6e6e9/Editor/Models/VFXGraph.cs:1467)
UnityEditor.VFX.UI.VFXViewWindow.Update () (at ./Library/PackageCache/com.unity.visualeffectgraph@ce719eb6e6e9/Editor/GraphView/VFXViewWindow.cs:384)
UnityEditor.HostView.SendUpdate () (at <85775034268147829a57676326841a5a>:0)
UnityEditor.EditorApplication.Internal_CallUpdateFunctions () (at <85775034268147829a57676326841a5a>:0){code}

Expected results: This console error spam shouldn't happen when opening the vfx.

This might be related to VFXGraph Custom Struct and Texture3D handling.