more graceful degradation of invalid unicode #7594

Job	Run time
Mac (Debug, clang, x86_64)	5m 24s
Mac (Debug, clang, arm64)	6m 21s
Windows (FastDebug, MSVC, Win32)	22m 38s
Mac (Release, clang, arm64)	9m 50s
Windows (Release, MSVC, x64)	23m 47s
Windows (Release, MSVC, Win32)	24m 11s
Windows (Debug, MSVC, Win32)	15m 1s
Windows (Debug, MSVC, x64)	15m 33s
Linux (Debug, gcc-9)	18m 41s
Linux (Debug, clang-16)	16m 17s
Linux (Release, gcc-13)	18m 28s
Linux (Release, clang-16)	21m 58s
Linux (Release, gcc-9)	25m 6s
Linux (Debug, gcc-13)	17m 11s
Linux (Release, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	17m 55s
Mac (Release, clang, x86_64)	8m 43s
Linux (Debug, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	15m 36s
Windows (FastDebug, MSVC, x64)	28m 1s
Linux (Release, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=ON)	18m 17s
Linux (Debug, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=ON)	15m 24s
	5h 44m 22s

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