[test] minor, fix -Weverything bot

test/fuzzing/main.cc

@@ -7,6 +7,7 @@
 int main (int argc, char **argv)
 {
   hb_blob_t *blob = hb_blob_create_from_file (argv[1]);
+
   unsigned int len;
   const char *font_data = hb_blob_get_data (blob, &len);
   if (len == 0)
@@ -15,7 +16,7 @@ int main (int argc, char **argv)
     exit (1);
   }
 
-  for (unsigned int i = 1; i < argc; i++)
+  for (int i = 1; i < argc; i++)
   {
     printf ("%s\n", argv[i]);
     LLVMFuzzerTestOneInput ((const uint8_t *) font_data, len);