checkpolicy, libsepol: Fix potential double free of mls_level_t #553

Job	Run time
build (gcc, 3.11, 3.1)	1m 33s
build (gcc, 3.11, 3.1, test-flags-override)	1m 18s
build (gcc, 3.11, 3.1, test-debug)	1m 29s
build (gcc, 3.11, 3.1, linker-bfd)	1m 31s
build (gcc, 3.11, 3.1, linker-gold)	1m 26s
build (gcc, 3.10, 3.1)	1m 42s
build (gcc, 3.9, 3.1)	1m 39s
build (gcc, 3.8, 3.1)	2m 5s
build (gcc, 3.7, 3.1)	1m 38s
build (gcc, pypy3.7, 3.1)	2m 8s
build (gcc, 3.11, 3.0)	1m 30s
build (gcc, 3.11, 2.7)	1m 41s
build (gcc, 3.11, 2.6)	1m 41s
build (gcc, 3.11, 2.5)	1m 43s
build (clang, 3.11, 3.1)	1m 45s
build (clang, 3.11, 3.1, test-flags-override)	1m 37s
build (clang, 3.11, 3.1, test-debug)	1m 30s
build (clang, 3.10, 3.1)	1m 39s
build (clang, 3.9, 3.1)	1m 52s
build (clang, 3.8, 3.1)	1m 37s
build (clang, 3.7, 3.1)	1m 40s
build (clang, pypy3.7, 3.1)	2m 36s
build (clang, 3.11, 3.0)	1m 39s
build (clang, 3.11, 2.7)	1m 53s
build (clang, 3.11, 2.6)	1m 55s
build (clang, 3.11, 2.5)	1m 51s
build (gcc, 3.11, 3.1, sanitizers)	1m 53s
	46m 31s

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