Comment 4 for bug 691600

Making the following change in line 93 of arMultiGetTransMatHull.cpp

 if( (hullTrackingMode==HULL_FOUR) && (numInPoints != 0))

gets the code running, resulting in the following output for the sample/multi code:

"0 good Markers found and used for pose estimation.
Pose-Matrix:
  0.00 0.00 0.00 0.00
  0.00 0.00 0.00 0.00
  0.00 0.00 0.00 0.00
  0.00 0.00 0.00 1.00"

Caveat: There may be better codepoints for checking for this condition, I'm not acquainted with the ARTKP code.