[set/map] Fix uninitialized memory

I keep forgetting that primitive types are NOT initialized during construction. :|

src/hb-map.hh

@@ -45,8 +45,8 @@ inline uint32_t Hash (const T &v)
 struct hb_map_t
 {
   HB_NO_COPY_ASSIGN (hb_map_t);
-  inline hb_map_t (void) { init_shallow (); }
-  inline ~hb_map_t (void) { fini_shallow (); }
+  inline hb_map_t (void) { init (); }
+  inline ~hb_map_t (void) { fini (); }
 
   struct item_t
   {

src/hb-object.hh

@@ -272,6 +272,7 @@ static inline void hb_object_fini (Type *obj)
   {
     user_data->fini ();
     free (user_data);
+    user_data = nullptr;
   }
 }
 template <typename Type>

src/hb-set.hh

@@ -40,8 +40,8 @@
 struct hb_set_t
 {
   HB_NO_COPY_ASSIGN (hb_set_t);
-  inline hb_set_t (void) { init_shallow (); }
-  inline ~hb_set_t (void) { fini_shallow (); }
+  inline hb_set_t (void) { init (); }
+  inline ~hb_set_t (void) { fini (); }
 
   struct page_map_t
   {