Refine errors for HTTP streaming. #1678

Job	Run time
utest-regression-blackbox-test	9m 34s
cygwin64-cache	1m 48s
multiple-arch-aarch64	22m 46s
multiple-arch-armv7	22m 13s
fast	1s
cygwin64	13m 54s
build-ubuntu16	3m 5s
build-cross-arm	5m 18s
build-cross-aarch64	5m 9s
build-ubuntu18	3m 4s
build-centos7	4m 58s
build-ubuntu20	3m 31s
coverage	3m 38s
multiple-arch-amd64	2m 15s
test-done	1s
	1h 41m 15s

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