Correctly catch "Invalid xsrfKey in request" error as "Not Signed In"

We were testing for the wrong exception type, resulting in this code
not matching the error message as we expected.  gwtjsonrpc throws an
InvocationException when the XSRF token is invalid.

Bug: GERRIT-265
Change-Id: Ifa7aa66f84c1d41a89ff3625975f52f6406da575
Signed-off-by: Shawn O. Pearce <sop@google.com>
1 file changed