gdbus: Remove not needed NULL pointer checks
gdbus: Remove not needed NULL pointer checks

g_strdup returns NULL if argument passed is NULL and there is no need
to double check that.

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