http/string: append need one more byte for null

src/plugins/http/src/httpParser.c

@@ -110,7 +110,7 @@ static void httpCleanupString(HttpString *str) {
 static int32_t httpAppendString(HttpString *str, const char *s, int32_t len) {
   if (str->size == 0) {
     str->pos = 0;
-    str->size = len;
+    str->size = len + 1;
     str->str = malloc(str->size);
   } else if (str->pos + len + 1 >= str->size) {
     str->size += len;