shared: Fix clearing of IO handlers
shared: Fix clearing of IO handlers

If NULL callback is passed to io_set_read/write_handler don't add watch
for it and just clear struct io memebers. This was resulting in
write/read_callback being call in loop due to fd being never written
or read.

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