How to reproduce:
1. Open attached "RTTest" project
2. Enter Play Mode

Expected result: Editor does not crash
Actual result: Editor crashes

Reproduced with: 2018.2.0a6, 2018.2.14f1, 2018.3.0b7, 2019.1.0a6
Does not reproduce with: 2017.4.14f1, 2018.2.0a5

Note: with versions earlier than 2018.2.0a6 Editor throws error:

"Attempting to release RenderTexture that were not gotten as a temp buffer
UnityEngine.RenderTexture:ReleaseTemporary(RenderTexture)
RTTest:Update() (at Assets/RTTest.cs:9)"
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Update: Fixed in 2019.1.0a10