perf cgroup: Avoid needless closing of unopened fd

Do not bother with close() if fd is not valid, just to silence valgrind:

    $ valgrind ./perf script
    ==59169== Memcheck, a memory error detector
    ==59169== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
    ==59169== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info
    ==59169== Command: ./perf script
    ==59169==
    ==59169== Warning: invalid file descriptor -1 in syscall close()
    ==59169== Warning: invalid file descriptor -1 in syscall close()
    ==59169== Warning: invalid file descriptor -1 in syscall close()
    ==59169== Warning: invalid file descriptor -1 in syscall close()
    ==59169== Warning: invalid file descriptor -1 in syscall close()
    ==59169== Warning: invalid file descriptor -1 in syscall close()
    ==59169== Warning: invalid file descriptor -1 in syscall close()
    ==59169== Warning: invalid file descriptor -1 in syscall close()
Signed-off-by: Tommi Rantala <tommi.t.rantala@nokia.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20200417132330.119407-1-tommi.t.rantala@nokia.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/cgroup.c

@@ -107,7 +107,8 @@ static int add_cgroup(struct evlist *evlist, const char *str)
 
 static void cgroup__delete(struct cgroup *cgroup)
 {
-	close(cgroup->fd);
+	if (cgroup->fd >= 0)
+		close(cgroup->fd);
 	zfree(&cgroup->name);
 	free(cgroup);
 }