Merge pull request #6352 from Goober5000/allow_explicitly_empty_sounds #685

Job	Run time
Linux (Debug, gcc-9)	10m 2s
Linux (Debug, gcc-13)	9m 4s
Linux (Debug, clang-16)	10m 46s
Linux (Release, gcc-9)	6m 49s
Linux (Release, gcc-13)	7m 44s
Linux (Release, clang-16)	10m 14s
Linux (Debug, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	8m 11s
Linux (Release, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	7m 13s
	1h 10m 3s

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