How to reproduce:
1. Create new project and have scene with some objects (mark static)
OR use the repro project attached in comment
3. Make sure that the scene is open, but Scene and Game windows are not visible
4. Open the Occlusion Culling window
5. Click the "Bake" button

Expected result: Occlusion window displays "Last bake: ..." baking information after baking process is over.
Actual result: Occlusion window displays "No occlusion data has been baked." instead (until Game windows is made visible).

Reproducible with - 2017.1.0a1, 2017.1.4f1, 2017.2.3f1, 2017.4.3f1, 2018.1.2f1, 2018.2.0b5

Notes:
- The issue is reproducible from any tab of the Occlusion Culling window.
- On some versions (those prior to 2018.1), to get the expected baking information, it is also necessary to hover over Occlusion Culling window or click somewhere in the Scene window.