crash when run in non-threaded mode

[stephanschulz]

i have used your great addon for multiple projects and it works great.

i wanted to test now how things work in non-threaded mode and noticed the same crash.

i have to admit i have not yet seen it happen in one of your example projects, only in my final app.
but the crash always points to the runLandmarkDetector()

it happens sometimes when it just lost a face.