How to reproduce:
1. Open the attached Unity project.
2. Open the sprite atlas named "CrashAtlas" in the Inspector window.
3. Press "Pack Preview".
4. Wait till sprite packing is finished.

Expected result: sprite atlas successfully packs the sprites.
Actual result: a message appears stating that Unity could not allocate memory. After closing the message, Unity crashes.

Reproducible with - 2017.1.0b5, 2017.1.3p4, 2017.2.2p4, 2017.4.2f2, 2018.1.0f2, 2018.2.0b3
Could not test with - 5.6.0a1, 5.6.6f2, 2017.1.0b4 (Sprite Atlas first introduced in 2017.1.0b5)

Note:
The crash happens when the sprite's max size is set to 4096 or 8192, sprite mode is multiple and there is a lot of sprites in it.