If sensors_data_poll failed the sensor thread would exit leaving
mThread non-null, hence SensorManager would never again attempt
to start the thread because it assumes that it's still running,
compromising future sensor notifications.
Original author: andih
Merged from: //branches/cupcake/...
Original author: android-build
Merged from: //branches/donutburger/...
Automated import of CL 143244
059c446fbf