Prevent starting multiple instances of MainActivity (fixes #943)
Prevent starting multiple instances of MainActivity (fixes #943)

Nutomic/syncthing-android,syncthing/syncthing-android,flipreverse/syncthing-android,jmintb/syncthing-android,jmintb/syncthing-android,syncthing/syncthing-android,syncthing/syncthing-android,flipreverse/syncthing-android,Nutomic/syncthing-android