Make SDL_ObjectValid() thread-safe #516

Job	Run time
Create test plan	4s
level1 / Haiku	2m 0s
level2 / Android (CMake, lean)	2m 45s
level2 / iOS (CMake & xcode)	2m 38s
level2 / Windows (msys2, ucrt64)	9m 0s
level2 / Android (Gradle)	2m 12s
level2 / Windows (msys2, mingw64)	9m 4s
level2 / Windows (MSVC, ARM64)	3m 41s
level2 / Windows (msys2, clang32)	7m 13s
level2 / RISC OS	1m 14s
level2 / Windows (MSVC, ARM)	3m 29s
level2 / Windows (msys2, clang64)	6m 17s
level2 / Windows (MSVC, x86)	5m 13s
level2 / Sony PlayStation Portable	3m 46s
level2 / Android (CMake)	2m 56s
level2 / Sony PlayStation Vita (GLES w/ PVR_PSP2)	3m 18s
level2 / Windows (MSVC, x64)	5m 34s
level2 / PowerPC64	2m 3s
level2 / Windows (MSVC, clang-cl x86)	5m 47s
level2 / NetBSD	2m 30s
level2 / Ubuntu 20.04 (Intel oneAPI)	6m 44s
level2 / Ubuntu 20.04	4m 2s
level2 / PowerPC	1m 49s
level2 / Sony PlayStation 2	4m 58s
level2 / Steam Linux Runtime (Sniper)	2m 58s
level2 / Android (Android.mk)	1m 14s
level2 / MacOS (Framework) (x64)	4m 17s
level2 / Windows (msys2, mingw32)	8m 43s
level2 / Ubuntu 22.04	4m 35s
level2 / Nintendo 3DS	2m 3s
level2 / Sony PlayStation Vita (GLES w/ pib)	3m 15s
level2 / GDK (MSVC, x64)	3m 6s
level2 / Windows (MSVC, clang-cl x64)	4m 30s
level2 / MacOS (Framework) (arm64)	2m 33s
level2 / FreeBSD	2m 48s
level2 / MacOS (GNU prefix)	3m 52s
level2 / Emscripten	9m 6s
level2 / Ubuntu 20.04 (Intel Compiler)	4m 32s
level2 / LoongArch64	2m 50s
level2 / tvOS (CMake & xcode)	2m 2s
	2h 40m 41s

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