perf machine: Destructors should accept NULL

And do nothing, just like free(), to avoid having to test it in callers,
usually in error paths.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-q42gj3b3znhho9z1mrbo4jce@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/machine.c

@@ -138,8 +138,10 @@ void machine__exit(struct machine *machine)
 
 void machine__delete(struct machine *machine)
 {
-	machine__exit(machine);
-	free(machine);
+	if (machine) {
+		machine__exit(machine);
+		free(machine);
+	}
 }
 
 void machines__init(struct machines *machines)

tools/perf/util/probe-event.c

@@ -102,10 +102,8 @@ out:
 
 void exit_probe_symbol_maps(void)
 {
-	if (host_machine) {
-		machine__delete(host_machine);
-		host_machine = NULL;
-	}
+	machine__delete(host_machine);
+	host_machine = NULL;
 	symbol__exit();
 }