http2: fix FileHandle leak in respondWithFile #3090

Job	Run time
Build slim tarball	1m 36s
x86_64-linux: with shared libraries	57m 7s
aarch64-linux: with shared libraries	1h 30m 25s
aarch64-darwin: with shared libraries	43m 22s
x86_64-darwin: with shared libraries	1h 6m 8s
	4h 18m 38s

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