gobex: fix checking connection id for ABORT
gobex: fix checking connection id for ABORT

OBEX spec state that it is optional to send a Connection Id header in an
OBEX ABORT operation.

Reported by Hendrik Sattler <post@hendrik-sattler.de>

pkarasev3/bluez,mapfau/bluez,ComputeCycles/bluez,pkarasev3/bluez,mapfau/bluez,silent-snowman/bluez,pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,silent-snowman/bluez,ComputeCycles/bluez,pstglia/external-bluetooth-bluez,silent-snowman/bluez,ComputeCycles/bluez,pkarasev3/bluez,mapfau/bluez,mapfau/bluez,silent-snowman/bluez,pkarasev3/bluez