GPUUploadManager: fix render-thread deadlock when upload stream reach… #4411

Job	Run time
Linux -> Pre-checks	22s
Linux -> Clang-x64, Release	13m 42s
Linux -> GCC-x64, Release	10m 15s
Linux -> Clang-NO_GLSLANG-x64, Debug	6m 37s
Linux -> Clang-NO_GLSLANG-NO_HLSL-x64, Release	5m 35s
Linux -> GCC-x64, Debug	12m 25s
Linux -> Clang-x64, Debug	14m 11s
	1h 3m 7s

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