aubinator: Don't skip the first field in each subgroup

The previous iteration algorithm would advance the field pointer right
after we advance the group.  This meant that you would end up with
skipping the first field of the group.  In the common case, where the
only field is a struct (e.g. 3DSTATE_VERTEX_BUFFERS), it would get
skipped entirely.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

src/intel/common/gen_decoder.c

@@ -824,14 +824,15 @@ iter_advance_group(struct gen_field_iterator *iter)
 static bool
 iter_advance_field(struct gen_field_iterator *iter)
 {
-   while (!iter_more_fields(iter)) {
+   if (iter_more_fields(iter)) {
+      iter->field = iter->field->next;
+   } else {
       if (!iter_more_groups(iter))
          return false;
 
       iter_advance_group(iter);
    }
 
-   iter->field = iter->field->next;
    if (iter->field->name)
       strncpy(iter->name, iter->field->name, sizeof(iter->name));
    else