fix mem leak #203

Job	Run time
clang-sanitizers (,thread)	1m 31s
downstream	27m 15s
clang-sanitizers (,address,undefined)	1m 22s
linux-compat (manylinux1-x64)	44s
linux-compiler-compat (clang-3)	1m 8s
linux-shared-libs	57s
linux-compat (manylinux1-x86)	51s
macos	36s
linux-compiler-compat (clang-6)	1m 30s
linux-compat (manylinux2014-x64)	1m 2s
linux-compiler-compat (clang-8)	1m 52s
linux-compat (manylinux2014-x86)	59s
linux-compiler-compat (clang-9)	1m 47s
macos-x64	55s
windows	1m 58s
linux-compat (fedora-34-x64)	46s
linux-compiler-compat (clang-10)	1m 22s
linux-compat (opensuse-leap)	57s
linux-compiler-compat (clang-11)	1m 24s
linux-compat (rhel8-x64)	43s
windows-app-verifier	3m 34s
linux-compiler-compat (gcc-4.8)	1m 8s
windows-shared-libs	1m 53s
linux-compat (al2-x64)	47s
linux-compiler-compat (gcc-5)	59s
linux-compiler-compat (gcc-6)	1m 2s
windows-vc14 (x86)	1m 40s
linux-compiler-compat (gcc-7)	59s
windows-vc14 (x64)	2m 27s
linux-compiler-compat (gcc-8)	1m 20s
	1h 5m 28s

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