log: UNLEAK rev to silence a large number of leaks

cmd_show populate rev with lots of data, and later returns without
cleaning it up. That's reasonable - we need this data until the process
completes - so we take the easy way out and UNLEAK it.

We have to add the UNLEAK early on, as cmd_show might return via
cmd_log_walk() in the next few lines, or it might continue to the
no-walk implementation below.

This patch silences the following leaks which were found when running
t0000 against LSAN:

Direct leak of 41 byte(s) in 1 object(s) allocated from:
    #0 0x486834 in strdup /home/abuild/rpmbuild/BUILD/llvm-11.0.0.src/build/../projects/compiler-rt/lib/asan/asan_interceptors.cpp:452:3
    #1 0x9ab168 in xstrdup /home/ahunt/oss-fuzz/git/wrapper.c:29:14
    #2 0x83cced in add_object_array_with_path /home/ahunt/oss-fuzz/git/object.c:349:17
    #3 0x8f4f5a in add_pending_object_with_path /home/ahunt/oss-fuzz/git/revision.c:329:2
    #4 0x8eb2b6 in handle_revision_arg_1 /home/ahunt/oss-fuzz/git/revision.c:2082:2
    #5 0x8eadad in handle_revision_arg /home/ahunt/oss-fuzz/git/revision.c:2089:12
    #6 0x8eea99 in setup_revisions /home/ahunt/oss-fuzz/git/revision.c:2756:7
    #7 0x59c024 in cmd_log_init_finish /home/ahunt/oss-fuzz/git/builtin/log.c:206:9
    git#8 0x5998d8 in cmd_log_init /home/ahunt/oss-fuzz/git/builtin/log.c:275:2
    git#9 0x599f9b in cmd_show /home/ahunt/oss-fuzz/git/builtin/log.c:641:2
    git#10 0x4cd92d in run_builtin /home/ahunt/oss-fuzz/git/git.c:453:11
    git#11 0x4cb5fa in handle_builtin /home/ahunt/oss-fuzz/git/git.c:704:3
    git#12 0x4ccf57 in run_argv /home/ahunt/oss-fuzz/git/git.c:771:4
    git#13 0x4caf49 in cmd_main /home/ahunt/oss-fuzz/git/git.c:902:19
    git#14 0x69ce3e in main /home/ahunt/oss-fuzz/git/common-main.c:52:11
    git#15 0x7f7c56197349 in __libc_start_main (/lib64/libc.so.6+0x24349)

Direct leak of 32 byte(s) in 1 object(s) allocated from:
    #0 0x49a9d2 in calloc /home/abuild/rpmbuild/BUILD/llvm-11.0.0.src/build/../projects/compiler-rt/lib/asan/asan_malloc_linux.cpp:154:3
    #1 0x9ab4c2 in xcalloc /home/ahunt/oss-fuzz/git/wrapper.c:140:8
    #2 0x59c269 in cmd_log_init_finish /home/ahunt/oss-fuzz/git/builtin/log.c:233:18
    #3 0x5998d8 in cmd_log_init /home/ahunt/oss-fuzz/git/builtin/log.c:275:2
    #4 0x599f9b in cmd_show /home/ahunt/oss-fuzz/git/builtin/log.c:641:2
    #5 0x4cd92d in run_builtin /home/ahunt/oss-fuzz/git/git.c:453:11
    #6 0x4cb5fa in handle_builtin /home/ahunt/oss-fuzz/git/git.c:704:3
    #7 0x4ccf57 in run_argv /home/ahunt/oss-fuzz/git/git.c:771:4
    git#8 0x4caf49 in cmd_main /home/ahunt/oss-fuzz/git/git.c:902:19
    git#9 0x69ce3e in main /home/ahunt/oss-fuzz/git/common-main.c:52:11
    git#10 0x7f7c56197349 in __libc_start_main (/lib64/libc.so.6+0x24349)

Indirect leak of 41 byte(s) in 1 object(s) allocated from:
    #0 0x486834 in strdup /home/abuild/rpmbuild/BUILD/llvm-11.0.0.src/build/../projects/compiler-rt/lib/asan/asan_interceptors.cpp:452:3
    #1 0x9ab168 in xstrdup /home/ahunt/oss-fuzz/git/wrapper.c:29:14
    #2 0x8f5e30 in add_rev_cmdline /home/ahunt/oss-fuzz/git/revision.c:1482:23
    #3 0x8eb26d in handle_revision_arg_1 /home/ahunt/oss-fuzz/git/revision.c:2081:2
    #4 0x8eadad in handle_revision_arg /home/ahunt/oss-fuzz/git/revision.c:2089:12
    #5 0x8eea99 in setup_revisions /home/ahunt/oss-fuzz/git/revision.c:2756:7
    #6 0x59c024 in cmd_log_init_finish /home/ahunt/oss-fuzz/git/builtin/log.c:206:9
    #7 0x5998d8 in cmd_log_init /home/ahunt/oss-fuzz/git/builtin/log.c:275:2
    git#8 0x599f9b in cmd_show /home/ahunt/oss-fuzz/git/builtin/log.c:641:2
    git#9 0x4cd92d in run_builtin /home/ahunt/oss-fuzz/git/git.c:453:11
    git#10 0x4cb5fa in handle_builtin /home/ahunt/oss-fuzz/git/git.c:704:3
    git#11 0x4ccf57 in run_argv /home/ahunt/oss-fuzz/git/git.c:771:4
    git#12 0x4caf49 in cmd_main /home/ahunt/oss-fuzz/git/git.c:902:19
    git#13 0x69ce3e in main /home/ahunt/oss-fuzz/git/common-main.c:52:11
    git#14 0x7fc4b3f06349 in __libc_start_main (/lib64/libc.so.6+0x24349)

Signed-off-by: Andrzej Hunt <andrzej@ahunt.org>

builtin/log.c

@@ -644,6 +644,7 @@ int cmd_show(int argc, const char **argv, const char *prefix)
 	opt.def = "HEAD";
 	opt.tweak = show_setup_revisions_tweak;
 	cmd_log_init(argc, argv, prefix, &rev, &opt);
+	UNLEAK(rev);
 
 	if (!rev.no_walk)
 		return cmd_log_walk(&rev);