Handle empty JSON token response errors.

Handle empty JSON token response errors.
Issue 96: https://code.google.com/p/google-oauth-java-client/issues/detail?id=96

[Anthony Moore, 2014-06-12 23:31:08]

I want to check first if we can solve this without the new virtual method.

https://codereview.appspot.com/108940044/diff/1/google-oauth-client/src/main/...
File
google-oauth-client/src/main/java/com/google/api/client/auth/oauth2/CredentialRefreshListener.java
(right):

https://codereview.appspot.com/108940044/diff/1/google-oauth-client/src/main/...
google-oauth-client/src/main/java/com/google/api/client/auth/oauth2/CredentialRefreshListener.java:86:
void onTokenErrorResponse(Credential credential, String tokenErrorResponse)
So, this feels like a disruptive and potentially breaking change that may be
disproportional for fixing a null reference error. It would be better to avoid
introducing new virtual methods here. Would it be possible to new up a dummy
TokenErrorResponse in this case so it can go through the original virtual call
instead?