Repro steps:
1. Open a VFX from the project folder that is not present in the scene
2. Make sure its Target GameObject window is closed
3. Drag the VFX in the scene
4. While it is still selected, open the Target GameObject window within the VFX Window
5. Observe that the Attach button is grayed out.
6. Select another object in the hierarchy and then click back on the VFX game object
7. Observe that the Attach button is now available.

Expected outcome:
When the Target GameObject window is opened to check if the currently selected game object contains a VisualEffect component and enable the attach button.

Note:
- Not a regression, existing behavior