FontInfo: Make sure that deleted member variables can no longer be used

Signed-off-by: Stefan Weil <sw@weilnetz.de>

src/ccstruct/fontinfo.cpp

@@ -2,7 +2,6 @@
 // File:        fontinfo.cpp
 // Description: Font information classes abstracted from intproto.h/cpp.
 // Author:      rays@google.com (Ray Smith)
-// Created:     Wed May 18 10:39:01 PDT 2011
 //
 // (C) Copyright 2011, Google Inc.
 // Licensed under the Apache License, Version 2.0 (the "License");
@@ -140,8 +139,10 @@ void FontInfoDeleteCallback(FontInfo f) {
   if (f.spacing_vec != nullptr) {
     f.spacing_vec->delete_data_pointers();
     delete f.spacing_vec;
+    f.spacing_vec = nullptr;
   }
   delete[] f.name;
+  f.name = nullptr;
 }
 void FontSetDeleteCallback(FontSet fs) {
   delete[] fs.configs;