How to reproduce:
1. Open the attached project
2. Open the "Main.unity" scene
3. Press Play
4. If Unity didn't crash, wait a bit

Actual result: Unity crashes.

Reproducible with: 2019.1.0a9, 2018.3.0b10, 2018.3.0a1.
Regression introduced in: 2018.3.0a1.
Not reproducible with: 2018.2.16f1, 2018.1.9f2, 2017.4.15f1

Notes:
The crash happens because NativeArray<T0>(T[] array, Unity.Collections.Allocator allocator); constructor gets an integer instead of an array.
The crash is not reproducible outside of subthread.

Error is thrown before the crash:
Assertion failed on expression: 'gCurrentManagedTempMem != NULL'

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Fixed in 2019.1.0a12, 2018.3.0b13.