Check if printf argument is NULL

In function ‘_print_xccdf_tailoring_header’,
    inlined from ‘_print_xccdf_tailoring’ at /home/jcerny/openscap/utils/oscap-info.c:279:2,
    inlined from ‘app_info_single_ds_profiles_only’ at /home/jcerny/openscap/utils/oscap-info.c:336:4,
    inlined from ‘app_info_single_ds’ at /home/jcerny/openscap/utils/oscap-info.c:513:18,
    inlined from ‘app_info_sds’ at /home/jcerny/openscap/utils/oscap-info.c:545:7,
    inlined from ‘app_info’ at /home/jcerny/openscap/utils/oscap-info.c:657:7:
/home/jcerny/openscap/utils/oscap-info.c:273:2: warning: ‘%s’ directive argument is null [-Wformat-overflow=]
  273 |  printf("%sBenchmark Hint: %s\n", prefix, xccdf_tailoring_get_benchmark_ref(tailoring));
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Author: jan-cerny

utils/oscap-info.c

@@ -270,7 +270,7 @@ static inline void _print_xccdf_tailoring_header(struct xccdf_tailoring *tailori
 	if (tailoring == NULL) {
 		return;
 	}
-	printf("%sBenchmark Hint: %s\n", prefix, xccdf_tailoring_get_benchmark_ref(tailoring));
+	printf("%sBenchmark Hint: %s\n", prefix ? prefix : "", xccdf_tailoring_get_benchmark_ref(tailoring));
 }
 
 static inline void _print_xccdf_tailoring(struct oscap_source *source, const char *prefix, void (*print_one_profile)(const struct xccdf_profile *, const char *))