[Android] Assert fails in internal Unreal Engine OpenGL ES code

[N7Alpha]

D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: === Critical error: ===
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: 
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: Assertion failed: ContextType >= 0 [File:D:/Build/++UE4/Sync/Engine/Source/Runtime/OpenGLDrv/Private/OpenGLDevice.cpp] [Line: 159] 
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: 
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A8DE8FCEC libUE4.so(0x0000000009686CEC)!FDebug::CheckVerifyFailedImpl(char const*, char const*, int, char16_t const*, ...)  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A92C27B90 libUE4.so(0x000000000E41EB90)!FOpenGLDynamicRHI::GetContextStateForCurrentContext(bool)  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A92CD6420 libUE4.so(0x000000000E4CD420)![Unknown]()  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A92C65D54 libUE4.so(0x000000000E45CD54)!RunOnGLRenderContextThread(TUniqueFunction<void ()>, bool)  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A92C84A2C libUE4.so(0x000000000E47BA2C)!FOpenGLDynamicRHI::RHIUpdateTexture2D(FRHITexture2D*, unsigned int, FUpdateTextureRegion2D const&, unsigned int, unsigned char const*)  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A8C9F39F0 libUE4.so(0x00000000081EA9F0)![Unknown]()  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A8C9F337C libUE4.so(0x00000000081EA37C)![Unknown]()  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A8C9E3904 libUE4.so(0x00000000081DA904)![Unknown]()  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A8C9E139C libUE4.so(0x00000000081D839C)!LibretroContext::core_video_refresh(void const*, unsigned int, unsigned int, unsigned int)  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A8CA12CDC libUE4.so(0x0000000008209CDC)![Unknown]()  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A8CA129B0 libUE4.so(0x00000000082099B0)![Unknown]()  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A8C9CF7F4 libUE4.so(0x00000000081C67F4)!UE4Function_Private::TFunctionRefBase<UE4Function_Private::TFunctionStorage<true>, void (void const*, unsigned int, unsigned int, unsigned long)>::operator()(void const*, unsigned int, unsigned int, unsigned long) const  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A8C9CFBBC libUE4.so(0x00000000081C6BBC)!func_wrap_video_refresh1(void const*, unsigned int, unsigned int, unsigned long)  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A82E5E8F0 5C54690809C44490B44B60F71570C51D.so(0x00000000000478F0)!retro_run()  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A8CA18264 libUE4.so(0x000000000820F264)![Unknown]()  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A8CA16230 libUE4.so(0x000000000820D230)![Unknown]()  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A8C9CA5E4 libUE4.so(0x00000000081C15E4)!UE4Function_Private::TFunctionRefBase<UE4Function_Private::TFunctionStorage<true>, void ()>::operator()() const  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A8C9CA594 libUE4.so(0x00000000081C1594)!FLambdaRunnable::Run()  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A8DD54E74 libUE4.so(0x000000000954BE74)!FRunnableThreadPThread::Run()  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007A8DC31D94 libUE4.so(0x0000000009428D94)!FRunnableThreadPThread::_ThreadProc(void*)  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007B3C775F48 libc.so(0x0000000000092F48)![Unknown]()  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: [Callstack] 0x0000007B3C706C88 libc.so(0x0000000000023C88)![Unknown]()  []
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: 
D/UE4     : [2022.02.06-19.29.00:669][  0]LogAndroid: Error: 

I'll fix this probably just documenting it here.

This crash happens immediately on loading an app with a OpenGL ES hardware accelerated core somewhat rarely like 1 in 10 startups. I suspect EGL might not be entirely threadsafe on Android, or Unreal does some jank where it probes threads and thinks the context I made is one used multithreaded rendering. The surrounding code in the assert suggests it could be something like that. I think if I just block in the Libretro Core thread's until Unreal Engine finishes loading all of its OpenGL ES context's that would probably workaround the issue in either case.