stream: fix TransformStream race on cancel with pending write #3875

Job	Run time
Build slim tarball	2m 9s
aarch64-darwin: with shared libraries	24m 50s
aarch64-linux: with shared libraries	21m 28s
x86_64-linux: with shared libraries	26m 25s
x86_64-darwin: with shared libraries	25m 37s
	1h 40m 29s

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