Merge Actors button is not enabled when selecting assets in the viewport if they are not visible in the Merge Actor window

The user has to scroll to the top of the Merge Actors window in order to enable the Merge Actors button even after selecting an actor in the level

1. Open any project in the editor
2. Open the Merge Actors window by going to Window->Developer Tools->Merge Actors
3. Size the Merge Actors window so it has a scroll bar
4. Drag two static meshes into the viewport
5. Scroll down in the Merge Actors window so you can not see the "Mesh components to be incorporated in the merge:" section
6. Right Click in the viewport and Unselect All
7. CTRL-click to select both static meshes

Result: Merge Actor button is disabled until the user scrolls back up to the top of the Merge Actors window

Expected: The Merge Actors button becomes enabled as soon as two static meshes are selected in the viewport