libselinux: set free'd data to NULL #578

Job	Run time
build (gcc, 3.12, 3.3)	1m 31s
build (gcc, 3.12, 3.3, test-flags-override)	1m 25s
build (gcc, 3.12, 3.3, test-debug)	1m 19s
build (gcc, 3.12, 3.3, linker-bfd)	1m 29s
build (gcc, 3.12, 3.3, linker-gold)	1m 27s
build (gcc, 3.11, 3.3)	1m 30s
build (gcc, 3.10, 3.3)	1m 33s
build (gcc, 3.9, 3.3)	1m 41s
build (gcc, 3.8, 3.3)	1m 39s
build (gcc, 3.7, 3.3)	1m 49s
build (gcc, pypy3.7, 3.3)	1m 57s
build (gcc, 3.12, 3.2)	1m 35s
build (gcc, 3.12, 3.1)	1m 32s
build (gcc, 3.12, 3.0)	1m 33s
build (gcc, 3.12, 2.7)	1m 44s
build (gcc, 3.12, 2.6)	1m 42s
build (gcc, 3.12, 2.5)	2m 6s
build (clang, 3.12, 3.3)	1m 36s
build (clang, 3.12, 3.3, test-flags-override)	1m 48s
build (clang, 3.12, 3.3, test-debug)	1m 37s
build (clang, 3.11, 3.3)	1m 40s
build (clang, 3.10, 3.3)	1m 45s
build (clang, 3.9, 3.3)	1m 41s
build (clang, 3.8, 3.3)	1m 41s
build (clang, 3.7, 3.3)	1m 41s
build (clang, pypy3.7, 3.3)	2m 7s
build (clang, 3.12, 3.2)	1m 33s
build (clang, 3.12, 3.1)	1m 42s
build (clang, 3.12, 3.0)	1m 44s
build (clang, 3.12, 2.7)	1m 49s
build (clang, 3.12, 2.6)	1m 46s
build (clang, 3.12, 2.5)	1m 53s
build (gcc, 3.12, 3.3, sanitizers)	2m 3s
	55m 38s

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