Keyboard navigation allows highlighting of crafter's output slot

The bug

Keyboard navigation allows highlighting of crafter's output slot, despite it not being selectable using the mouse cursor.

How to reproduce

1. Place a crafter.

2. Move the cursor to the output slot.

3. Try this again but using keyboard navigation.

Expected result

The crafter output slot would not get highlighted using keyboard navigation.

Observed result

The slot is highlighted despite this not being possible with the mouse cursor.