[subset-input] Fix leak

src/hb-subset-input.hh

@@ -86,6 +86,9 @@ struct hb_subset_input_t
 
   ~hb_subset_input_t ()
   {
+    for (auto& set : sets_iter ())
+      set = hb::shared_ptr<hb_set_t> ();
+
 #ifdef HB_EXPERIMENTAL_API
     for (auto _ : name_table_overrides)
       _.second.fini ();