[subset] Simplify recent out-of-memory fixes

By checking return status of map->set().
diff --git a/src/hb-ot-layout-gsubgpos.hh b/src/hb-ot-layout-gsubgpos.hh
index 1e9f2f4..f820976 100644
--- a/src/hb-ot-layout-gsubgpos.hh
+++ b/src/hb-ot-layout-gsubgpos.hh
@@ -108,12 +108,12 @@
 
       if (!done_lookups_glyph_set->get (lookup_index))
       {
-        hb_set_t* empty_set = hb_set_create ();
-        done_lookups_glyph_set->set (lookup_index, empty_set);
-        if (!done_lookups_glyph_set->get (lookup_index)) {
-          hb_set_destroy (empty_set);
-          return true;
-        }
+	hb_set_t* empty_set = hb_set_create ();
+	if (unlikely (!done_lookups_glyph_set->set (lookup_index, empty_set)))
+	{
+	  hb_set_destroy (empty_set);
+	  return true;
+	}
       }
 
       done_lookups_glyph_set->get (lookup_index)->clear ();