"Scene(s) Have Been Modified" popup window occupies all display height when there are multiple changed scenes

Steps to repro:

1. Open the attached project and 'main' scene;
2. Drag all the scenes from the 'Scenes' folder to the Hierarchy;
2. Open 'Lighting' window (Window>Lighting>Settings);
3. In the Lighting window click 'Generate Lighting' button;
4. Wait until lighting is generated;
5. Close the Editor.

Actual result:
"Scene(s) Have Been Modified" popup window occupies all display height when there are multiple changed scenes (see attached actual.png screenshot). As a result, there is no ability to save/not save modified scenes.The only workaround is to close the popup with Escape button and save the project.

Expected result:
Text in the popup window should be clamped to several strings if there are changes in multiple scenes and not to occupy all display space.

Notes:
- Reproducible in 2018.2.0a1, 2018.1.0b7, 2017.3.0p2.
- Reproducible on Windows;
- The issue happens only when there are lots of unsaved scenes in the Project.