obexd: Fix crash while session shutdown
obexd: Fix crash while session shutdown

g_str_equal has been used for the session path compare
which is not NULL-safe. Used the g_strcmp0() for the NULL-Safe
string comparision.

*#0 strcmp (p1=0x0, p2=0x7105c "/org/bluez/obex/client/session0")
*    at strcmp.c:38
*#1  0xb6e0cd0a in g_str_equal (v1=<value optimized out>,
*    v2=<value optimized out>) at ghash.c:1704
*#2  0x000264d8 in find_session (connection=<value optimized out>,
*    message=0x55b38, user_data=<value optimized out>)
*    at obexd/client/manager.c:162
*#3  remove_session (connection=<value optimized out>, message=0x55b38,
    user_data=<value optimized out>) at obexd/client/manager.c:231

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