send silence when no data is captured (#272) #927

Job	Run time
Build (x86_64-pc-windows-msvc)	5m 51s
Build (aarch64-pc-windows-msvc)	6m 12s
Build (x86_64-apple-darwin)	8m 20s
Build (aarch64-apple-darwin)	8m 5s
Build (aarch64-apple-ios)	8m 21s
Build (aarch64-apple-ios-sim)	9m 36s
Build (x86_64-unknown-linux-gnu)	3m 40s
Build (aarch64-unknown-linux-gnu)	5m 2s
Build (aarch64-linux-android)	3m 40s
Build (armv7-linux-androideabi)	3m 52s
Build (x86_64-linux-android)	3m 41s
	1h 6m 20s

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