Fix new -Wnull-conversion violations detected by a newer clang.

chrome/common/zip_reader.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 "chrome/common/zip_reader.h"
 
 #include "base/file_util.h"
 #include "base/logging.h"
 #include "base/string_util.h"
 #include "base/utf_string_conversions.h"
@@ skipping 130 matching lines @@
   char raw_file_name_in_zip[internal::kZipMaxPath] = {};
   const int result = unzGetCurrentFileInfo(zip_file_,
                                            &raw_file_info,
                                            raw_file_name_in_zip,
                                            sizeof(raw_file_name_in_zip) - 1,
                                            NULL,  // extraField.
                                            0,  // extraFieldBufferSize.
                                            NULL,  // szComment.
                                            0);  // commentBufferSize.
   if (result != UNZ_OK)
-    return NULL;
+    return false;
   if (raw_file_name_in_zip[0] == '\0')
-    return NULL;
+    return false;
   current_entry_info_.reset(
       new EntryInfo(raw_file_name_in_zip, raw_file_info));
   return true;
 }
 
 bool ZipReader::LocateAndOpenEntry(const FilePath& path_in_zip) {
   DCHECK(zip_file_);
 
   current_entry_info_.reset();
   reached_end_ = false;
@@ skipping 124 matching lines @@
 }
 
 void ZipReader::Reset() {
   zip_file_ = NULL;
   num_entries_ = 0;
   reached_end_ = false;
   current_entry_info_.reset();
 }
 
 }  // namespace zip