Fix crash issues if there is no resources pack in content shell

ui/base/resource/data_pack.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/base/resource/data_pack.h"
 
 #include <errno.h>
 #include <utility>
 
 #include "base/files/file_util.h"
@@ skipping 172 matching lines @@
   // bothering to do right now.
 #if defined(__BYTE_ORDER)
   // Linux check
   static_assert(__BYTE_ORDER == __LITTLE_ENDIAN,
                 "datapack assumes little endian");
 #elif defined(__BIG_ENDIAN__)
   // Mac check
   #error DataPack assumes little endian
 #endif
 
+  if (!mmap_)
+    return false;
+
   const DataPackEntry* target = reinterpret_cast<const DataPackEntry*>(
       bsearch(&resource_id, mmap_->data() + kHeaderLength, resource_count_,
               sizeof(DataPackEntry), DataPackEntry::CompareById));
   if (!target) {
     return false;
   }
 
   const DataPackEntry* next_entry = target + 1;
   // If the next entry points beyond the end of the file this data pack's entry
   // table is corrupt. Log an error and return false. See
@@ skipping 142 matching lines @@
       return false;
     }
   }
 
   base::CloseFile(file);
 
   return true;
 }
 
 }  // namespace ui