winbindd-irpc: Ensure not to call irpc_send_reply twice on error

winbindd-irpc: Ensure not to call irpc_send_reply twice on error

As found during investigation of the previous commit, when the RPC
call fails totally, we must only try and send one error reply.

Andrew Bartlett

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Signed-off-by: Garming Sam <garming@catalyst.net.nz>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Pair-programmed-with: Garming Sam <garming@catalyst.net.nz>

Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Fri Aug  1 12:11:29 CEST 2014 on sn-devel-104