Fix mg_sntp_parse()

test/fuzz.c

@@ -4,25 +4,32 @@
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
   struct mg_dns_message dm;
   mg_dns_parse(data, size, &dm);
+  mg_dns_parse(NULL, 0, &dm);
 
   struct mg_http_message hm;
   mg_http_parse((const char *) data, size, &hm);
+  mg_http_parse(NULL, 0, &hm);
 
   struct mg_str body = mg_str_n((const char *) data, size);
   char tmp[256];
   mg_http_get_var(&body, "key", tmp, sizeof(tmp));
   mg_url_decode((char *) data, size, tmp, sizeof(tmp), 1);
   mg_url_decode((char *) data, size, tmp, 1, 1);
+  mg_url_decode(NULL, 0, tmp, 1, 1);
 
   struct mg_mqtt_message mm;
   mg_mqtt_parse(data, size, &mm);
+  mg_mqtt_parse(NULL, 0, &mm);
 
   struct timeval tv;
   mg_sntp_parse(data, size, &tv);
+  mg_sntp_parse(NULL, 0, &tv);
 
   char buf[size * 4 / 3 + 5];  // At least 4 chars and nul termination
   mg_base64_decode((char *) data, size, buf);
+  mg_base64_decode(NULL, 0, buf);
   mg_base64_encode(data, size, buf);
+  mg_base64_encode(NULL, 0, buf);
 
   return 0;
 }