Check for existing token during two-factor login

OAuth2 token notes must be unique so without this check a
login from a 2nd device will fail when it tries to create an
authorization and one already exists.

app/src/main/java/com/github/mobile/accounts/TwoFactorAuthActivity.java

@@ -221,7 +221,9 @@ public User call() throws Exception {
                 client.setOtpCode(otpCode);
 
                 OAuthService service = new OAuthService(client);
-                String authToken = AccountAuthenticator.createAuthorization(service);
+                String authToken = AccountAuthenticator.getAuthorization(service);
+                if (authToken == null)
+                  authToken = AccountAuthenticator.createAuthorization(service);
                 client.setOAuth2Token(authToken);
 
                 User user = new UserService(client).getUser();
@@ -257,4 +259,4 @@ public void onSuccess(User user) {
         };
         authenticationTask.execute();
     }
-}
+}

app/src/main/java/com/github/mobile/accounts/TwoFactorAuthClient.java

@@ -71,6 +71,9 @@ public void setOtpCode(String otpCode) {
     @Override
     public GitHubResponse get(GitHubRequest request) throws IOException {
         HttpURLConnection httpRequest = createGet(request.generateUri());
+        if (!TextUtils.isEmpty(otpCode))
+            httpRequest.setRequestProperty(HEADER_OTP, otpCode);
+
         try {
             String accept = request.getResponseContentType();
             if (accept != null)
@@ -147,4 +150,4 @@ private <V> V sendJson(final HttpURLConnection request,
         throw createException(getStream(request), code,
                 request.getResponseMessage());
     }
-}
+}