Mobile: Setup screen isn't always popping up when an external device is needed

[markus-ebner]

Occasionally, the setup screen isn't shown on first start up when having a study where an external bluetooth device is needed.
It occurred on iOS with a Polar HR study, but not Android.

• Check, if it always comes up.
• If not, try to locate and fix the problem.

[janoliver20]

Maybe fixed with #350