Fix: wrong check after malloc in buffer registry

Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: consumer add channel return value was positive on error

Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>
Destroy channel on relayd/sessiond send error

Signed-off-by: David Goulet <dgoulet@efficios.com>