example1 should check return value of flandmark_detect

[penguin42]

Hi, in example1.cpp the main loop does:

    flandmark_detect(input, bbox, model, landmarks);

and then goes on to plot the results; however on one of my images (which doesn't actually contain any faces) a face is wrongly detected by the HaarDetect but then the flandmark_detect flags an error. which is ignored and you still end up plotting the values - these tend to be the old values from the previous loop and thus you don't notice, but the values can be completely bogus.