perf evsel: Use zfree() to reduce chances of use after free

Do defensive programming by using zfree() to initialize freed pointers
to NULL, so that eventual use after free result in a NULL pointer deref
instead of more subtle behaviour.

Also remove one NULL test before free(), as it accepts a NULL arg and we
get one line shaved not doing it explicitely.
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evsel.c

@@ -2917,8 +2917,7 @@ bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize)
 		if (asprintf(&new_name, "%s%su", name, sep) < 0)
 			return false;
 
-		if (evsel->name)
-			free(evsel->name);
+		free(evsel->name);
 		evsel->name = new_name;
 		scnprintf(msg, msgsize, "kernel.perf_event_paranoid=%d, trying "
 			  "to fall back to excluding kernel and hypervisor "
@@ -3156,7 +3155,7 @@ void evsel__zero_per_pkg(struct evsel *evsel)
 
 	if (evsel->per_pkg_mask) {
 		hashmap__for_each_entry(evsel->per_pkg_mask, cur, bkt)
-			free((void *)cur->pkey);
+			zfree(&cur->pkey);
 
 		hashmap__clear(evsel->per_pkg_mask);
 	}