[subset] fix memory leaks found in https://oss-fuzz.com/testcase-detail/5179935334465536

src/hb-repacker.hh

@@ -147,6 +147,7 @@ struct graph_t
       }
 
       vertex_t* v = vertices_.push ();
+      if (check_success (!vertices_.in_error ()))
         v->obj = *objects[i];
       if (!removed_nil) continue;
       for (unsigned i = 0; i < v->obj.links.length; i++)

src/hb-vector.hh

@@ -177,6 +177,11 @@ struct hb_vector_t
   Type *push (T&& v)
   {
     Type *p = push ();
+    if (p == &Crap (Type))
+      // If push failed to allocate then don't copy v, since this may cause
+      // the created copy to leak memory since we won't have stored a
+      // reference to it.
+      return p;
     *p = hb_forward<T> (v);
     return p;
   }