How to reproduce:
1. Open the attached 'test-packages-2d.zip' project
2. Select Assets -> Test -> 'ExplosionSprite' Sprite
3. Open Sprite Editor
4. Drag away top-right Sprite's rectangles
5. Select Slice menu in the control bar
6. Select Safe in the Method dropdown
7. Press the Slice button

Expected result: The top-right Sprite's bottom is not included in the sliced rectangle
Actual result: The top-right Sprite's bottom is included in the sliced rectangle

Reproducible with: 2017.4.33f1, 2018.4.12f1, 2019.2.11f1 (1.0.0), 2019.3.0b8 (1.0.0), 2020.1.0a9 (1.0.0)

Notes:
- 2017.4, 2018.4 Sprite Editor is not included in the package
- If Sprite was sliced by Smart Slicing Method first and then sliced by the Safe Slicing Method, the bigger top-right Sprite's part is not sliced