Do not try to decrypt empty refresh token

Calling DecryptWithSystemSalt() with an empty string results in a WARNING in the log.

BUG=393341

Review URL: https://codereview.chromium.org/384383002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@282943 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/chromeos/settings/device_oauth2_token_service.cc

@@ -235,14 +235,16 @@ void DeviceOAuth2TokenService::DidGetSystemSalt(
   // Otherwise, load the refresh token from |local_state_|.
   std::string encrypted_refresh_token =
       local_state_->GetString(prefs::kDeviceRobotAnyApiRefreshToken);
+  if (!encrypted_refresh_token.empty()) {
     CryptohomeTokenEncryptor encryptor(system_salt_);
     refresh_token_ = encryptor.DecryptWithSystemSalt(encrypted_refresh_token);
-  if (!encrypted_refresh_token.empty() && refresh_token_.empty()) {
+    if (refresh_token_.empty()) {
       LOG(ERROR) << "Failed to decrypt refresh token.";
       state_ = STATE_NO_TOKEN;
       FireRefreshTokensLoaded();
       return;
     }
+  }
 
   state_ = STATE_VALIDATION_PENDING;