To reproduce:
1. Open project
2. Select 'test1' sprite
3. Change its sprite mode to single, apply changes
4. Change its sprite mode back to multiple, apply changes
5. Open sprite editor
6. Mark sprite, trim, apply changes
7. Open 'test2' in the sprite editor
8. Mark sprite, apply changes, press trim button

Expected: no errors will be thrown
Actual: IndexOutOfRangeException is thrown

Reproduced: 2017.2.2p1, 2017.3.2f1, 2018.1.0b13, 2018.2.0b8
Not reproducible: 5.6.5p2, 2017.1.3p2 (in these versions trim button becomes greyed out after applying changes)

Note: on some versions issue is reproducible only on freshly downloaded(not modified) repro project