gobex: fix transfer search in transfer_complete
gobex: fix transfer search in transfer_complete

The previous approach searched the transfer pointer itself, assuming
that the transfers has not been modified if the pointer is in the list.
However the callback could have removed the transfer and registered
another one, which can eventually point to the same memory location.

This is solved by looking for the transfer id instead of the pointer.

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