Reorder finalization to avoid potential crash; ref #4618

`mrb_gc_destroy` may call other mruby API functions from the finalizers.
So call that function first.

src/state.c

@@ -221,10 +221,10 @@ mrb_close(mrb_state *mrb)
   }
 
   /* free */
-  mrb_gc_free_gv(mrb);
-  mrb_free_context(mrb, mrb->root_c);
-  mrb_free_symtbl(mrb);
   mrb_gc_destroy(mrb, &mrb->gc);
+  mrb_free_context(mrb, mrb->root_c);
+  mrb_gc_free_gv(mrb);
+  mrb_free_symtbl(mrb);
   mrb_free(mrb, mrb);
 }