core/gatt: Fix crash when running without -E
core/gatt: Fix crash when running without -E

btd_gatt_database_new should not fail if it is unable to register
GattManager interface since it is experimental.

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