http2: fix FileHandle leak in respondWithFile #3084

Job	Run time
Build slim tarball	1m 33s
aarch64-darwin: with shared libraries	47m 54s
aarch64-linux: with shared libraries	1h 27m 48s
x86_64-linux: with shared libraries	56m 45s
x86_64-darwin: with shared libraries	1h 32m 54s
	4h 46m 54s

Provide feedback