core: Fix g_source_remove() with zero ID while removing device

core: Fix g_source_remove() with zero ID while removing device

store_device_info_cb() is also used as callback for g_idle_add() and
therefore sets device->store_id to zero. During device removal it may be
called manually, which must be done only after the existing
device->store_id is removed from mainloop.

Fix this GLib error (and a bunch of invalid read/writes when
store_device_info_cb() was called after device removal due to this bug):

bluetoothd[1192]: src/device.c:device_remove() Removing device
/org/bluez/hci0/dev_12_34_12_34_12_34

(bluetoothd:1192): GLib-CRITICAL **: g_source_remove: assertion `tag >
0' failed
bluetoothd[1192]: src/device.c:btd_device_unref() Freeing device
/org/bluez/hci0/dev_12_34_12_34_12_34
bluetoothd[1192]: src/device.c:device_free() 0x463a2a0