How to reproduce:
1. Create two VFX Graphs in Project Browser
2. Open them both
3. Delete them both from project browser in order to get empty vfx windows
4. Press "Create a new Visaul Effect Graph" in vfx window
5. Try to open newly created VFX

Expected result: VFX graph window opens
Actual result: text file opens and errors are thrown to the console

Reproduced with: 2022.1.0a16 (Graphics master from 2021/11/22)

Notes:
- Can not reproduce with one VFX window
- Closing all the windows opens VFX Graph as supposed to
- Error messages:
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.VFX.UI.VFXViewWindow+<>c__DisplayClass7_0.<GetWindow>b__0 (UnityEditor.VFX.UI.VFXViewWindow x) (at com.unity.visualeffectgraph/Editor/GraphView/VFXViewWindow.cs:66)

Exception thrown while invoking [OnOpenAssetAttribute] method 'VisualEffectAssetEditor:OnOpenVFX (int,int)' : NullReferenceException: Object reference not set to an instance of an object
UnityEditor.VFX.UI.VFXViewWindow+<>c__DisplayClass6_0.<GetWindow>b__0 (UnityEditor.VFX.UI.VFXViewWindow x) (atcom.unity.visualeffectgraph/Editor/GraphView/VFXViewWindow.cs:60)