How to reproduce:
1. Open the attached project named Case_1300770"
2. Select the New Custom Render Texture in the Project Window
3. Under the Material section, change the used shader from Unlit/TestShader to Unlit/Transparent

Expected result: Shader of the Render Texture is changed or an error is thrown if some incompatibilities are present
Actual result: Editor crashes with

Reproducible with: 2018.4.30f1, 2019.4.17f1, 2020.1.17f1, 2020.2.1f1, 2021.1.0a11

Relevant information from the Editor logs:

Assertion failed on expression: 'pass >= 0 && pass < (int)m_Passes.size()'

Material::SetPassFast called with NULL shader pass

Received signal SIGSEGV
Stack trace:
0x00007ff7a3d2ae28 (Unity) ApplyMaterialPassWithCache
0x00007ff7a3d69051 (Unity) Material::SetPassSlowWithShader
0x00007ff7a3ba6cfd (Unity) CustomRenderTextureManager::UpdateCustomRenderTexture
0x00007ff7a3ba6ff7 (Unity) CustomRenderTextureManager::UpdateCustomRenderTextures
0x00007ff7a3ba68e6 (Unity) CustomRenderTextureManager::Update
0x00007ff7a3cbd3b9 (Unity) `InitPlayerLoopCallbacks'::`2'::PostLateUpdateUpdateCustomRenderTexturesRegistrator::Forward
0x00007ff7a3ca644c (Unity) ExecutePlayerLoop
0x00007ff7a3ca6523 (Unity) ExecutePlayerLoop
0x00007ff7a3cab639 (Unity) PlayerLoop
0x00007ff7a441f231 (Unity) PlayerLoopController::UpdateScene
0x00007ff7a441d801 (Unity) Application::TickTimer
0x00007ff7a4818af1 (Unity) MainMessageLoop
0x00007ff7a481c786 (Unity) WinMain
0x00007ff7a6377172 (Unity) __scrt_common_main_seh
0x00007fff68167c24 (KERNEL32) BaseThreadInitThunk
0x00007fff68dcd4d1 (ntdll) RtlUserThreadStart