Coverity: Add a missing NULL check.

BUG=none
TEST=none
CID=16813

Review URL: http://codereview.chromium.org/7216034

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@89991 0039d316-1c4b-4281-b951-d872f2087c98
bool ExtensionPrefs::ReadExtensionPrefBoolean(
    const std::string& extension_id, const std::string& pref_key) {
  const DictionaryValue* ext = GetExtensionPref(extension_id);
  if (!ext) {
    return false;
  }
  return ReadBooleanFromPref(ext, pref_key);
}

bool ExtensionPrefs::ReadExtensionPrefBoolean(
    const std::string& extension_id, const std::string& pref_key) {
  const DictionaryValue* ext = GetExtensionPref(extension_id);
  if (!ext) {
    return false;
  }
  return ReadBooleanFromPref(ext, pref_key);
}
