[FIX] invitation page displays null when no nickname is available

Trivial fix, just use the base part of the JID when no nickname is
available.

Change-Id: I3a4c4b72081ce91c5ee6c0ac5ae005e0714ba398
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1261
Reviewed-by: Nils Bussas <nils.bussas@gmail.com>
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>
[BUILD] Prepared Beta-Update site for 13.12.6

The version number is 13.12.6.TESTING

Change-Id: Ibbbad392792a9f2fd9ba9868d5f24a874d85f0a4
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1285
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>