core: don't report an big OS error when the insert comes from the user

If the "reason" for inserting an object is NULL, dont report
a big user-visible OS error warning. Just let the caller warn
when it gets an error code and if it wants to warn.
That's what lstopo --ps does when it fails to insert a group
for attaching a Misc for showing task binding.

Valentin properly handled this case during the callback->reason
conversion but I removed it mistake when I pushed all this as
commit 0dce1af

Thanks to Philippe Swartvagher for the report.

Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>

hwloc/topology.c

@@ -111,7 +111,7 @@ static void report_insert_error(hwloc_obj_t new, hwloc_obj_t old, const char *ms
   report_insert_error_format_obj(newstr, sizeof(newstr), new);
   report_insert_error_format_obj(oldstr, sizeof(oldstr), old);
 
-  if (!reported && !hwloc_hide_errors()) {
+  if (reason && !reported && !hwloc_hide_errors()) {
     fprintf(stderr, "****************************************************************************\n");
     fprintf(stderr, "* hwloc %s received invalid information from the operating system.\n", HWLOC_VERSION);
     fprintf(stderr, "*\n");