Fix crash due to BLE sensor data reported after shutdown

[dennisguse]

Problem(s):

• TrackListActivity started sensors and recording (always).
• The TrackRecordingService checked only if a recording was running and NOT if the sensors were already started.

Follow-up:

• Shutdown of sensors may not been correct for quite a while
• Sensor data shouldn't have been affected

Moreover: TrackListActivity's start and stop sensor didn't work correctly.

[Mats391]

I tested the latest nightly including this fix with my heart rate sensor and it no longer crashes. I restarted recording and the app multiple times and it worked in all tests.