stream: fix writev unhandled rejection in fromWeb #4328

Job	Run time
Build slim tarball	2m 30s
aarch64-linux: with shared libraries	17m 30s
x86_64-darwin: with shared libraries	42m 3s
aarch64-darwin: with shared libraries	20m 5s
x86_64-linux: with shared libraries	19m 58s
	1h 42m 6s

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