Fix `use after free in File#initilialize_copy`; fix #4001

The bug and the fix were reported by https://hackerone.com/pnoltof

mrbgems/mruby-io/src/io.c

@@ -561,13 +561,13 @@ mrb_io_initialize_copy(mrb_state *mrb, mrb_value copy)
   mrb_bool failed = TRUE;
 
   mrb_get_args(mrb, "o", &orig);
+  fptr_orig = io_get_open_fptr(mrb, orig);
   fptr_copy = (struct mrb_io *)DATA_PTR(copy);
   if (fptr_copy != NULL) {
     fptr_finalize(mrb, fptr_copy, FALSE);
     mrb_free(mrb, fptr_copy);
   }
   fptr_copy = (struct mrb_io *)mrb_io_alloc(mrb);
-  fptr_orig = io_get_open_fptr(mrb, orig);
 
   DATA_TYPE(copy) = &mrb_io_type;
   DATA_PTR(copy) = fptr_copy;