fix zero size zchunk #2297 #151

Job	Run time
build (ubuntu-20.04, default, enabled, clang-format-11, automake autoconf clang-format-11 git uui...	4m 30s
build (ubuntu-20.04, default, disabled, clang-format-11, automake autoconf clang-format-11 git uu...	3m 7s
build (ubuntu-20.04, valgrind, enabled, automake autoconf valgrind git uuid-dev libsystemd-dev li...	2m 44s
build (ubuntu-20.04, cmake, enabled, cmake git uuid-dev libsystemd-dev liblz4-dev libnss3-dev lib...	1m 32s
build (macos-latest, default, automake autoconf libtool ossp-uuid zeromq curl libmicrohttpd, ena...	3m 14s
build (macos-latest, default, disabled, automake autoconf libtool ossp-uuid zeromq curl libmicro...	2m 56s
build (ubuntu-20.04, cmake, 1, clang-format-11, cmake clang-format-11 git uuid-dev libsystemd-dev...	36s
build (ubuntu-20.04, abi-compliance-checker, universal-ctags abi-dumper abi-compliance-checker gi...	1m 9s
build (ubuntu-20.04, check_zproject, git uuid-dev libsystemd-dev liblz4-dev libnss3-dev libzmq3-d...	48s
	20m 36s

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