ref-filter: also free head for ATOM_HEAD to avoid leak
u.head is populated using resolve_refdup(), which returns a newly
allocated string - hence we also need to free() it.
Found while running t0041 with LSAN:
Direct leak of 16 byte(s) in 1 object(s) allocated from:
#0 0x486804 in strdup ../projects/compiler-rt/lib/asan/asan_interceptors.cpp:452:3
#1 0xa8be98 in xstrdup wrapper.c:29:14
#2 0x9481db in head_atom_parser ref-filter.c:549:17
#3 0x9408c7 in parse_ref_filter_atom ref-filter.c:703:30
#4 0x9400e3 in verify_ref_format ref-filter.c:974:8
#5 0x4f9e8b in print_ref_list builtin/branch.c:439:6
#6 0x4f9e8b in cmd_branch builtin/branch.c:757:3
#7 0x4ce83e in run_builtin git.c:475:11
#8 0x4ccafe in handle_builtin git.c:729:3
#9 0x4cb01c in run_argv git.c:818:4
#10 0x4cb01c in cmd_main git.c:949:19
#11 0x6bdc2d in main common-main.c:52:11
#12 0x7f96edf86349 in __libc_start_main (/lib64/libc.so.6+0x24349)
SUMMARY: AddressSanitizer: 16 byte(s) leaked in 1 allocation(s).
Signed-off-by: Andrzej Hunt <andrzej@ahunt.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>