[INTERNAL] properly initialized XMPPAccountStore

Change-Id: I8b9e86225d240230e41e575c13ed5edbc249ca7e
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1798
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>
Reviewed-by: Holger Schmeisky <google@schmeisky.com>