Merge pull request #6352 from Goober5000/allow_explicitly_empty_sounds #1693

Job	Run time
Linux (Debug, gcc-9)	11m 9s
Linux (Debug, gcc-13)	8m 48s
Linux (Debug, clang-16)	10m 43s
Linux (Release, gcc-9)	6m 51s
Linux (Release, gcc-13)	7m 36s
Linux (Release, clang-16)	10m 27s
Linux (Debug, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	8m 7s
Linux (Release, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	7m 26s
	1h 11m 7s

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